Practical Manuel
MBBS
Phase I
DEPARTMENT OF BIOCHEMISTRY
FACULTY OF MEDICAL SCIENCES
UNIVERSITY OF SRI JAYEWARDENEPURA
2011
1
BIOCHEMISTRY PRACTICALS
The Biochemistry practical manual is for the undergraduates during the
Phase 1 of the MBBS degree course. The manual contains the procedures
of laboratory practicals as well as the contents of the guided learning
sessions (GLS)/ fixed learning modules (FLM) that will be carried out in
the Department of Biochemistry under different modules.
2
TABLE OF CONTENTS
1st Term
Foundation Module
 Practical 1 - Introduction to Laboratory
 Practical 2 - Cell, pH and buffers
 Practical 3 - Tests for Carbohydrates and Lipids
 Practical 4 - Tests for Amino acids and Proteins
 Practical 5 - Enzymology I
 Practical 6 - Enzymology II
3rd Term
Metabolism, Endocrine and Nutrition Module
 GLS 1 – Introduction to Disorders of Carbohydrates and Lipid Metabolism
 GLS 2 - Catabolism and Excretion of Nitrogenous Compounds
 FLM – Thyroid Hormones
 GLS 3 – Diabetes Mellitus
 GLS 4 – Introduction to Endocrine Disorders
 Practical 7 – Determination of Glucose in Urine and Serum
 Practical 8 – Diet
Gastro Intestinal Tract Module
 Practical 9– Estimation of liver enzymes and constituents of bile.
4th Term
Renal Module
 Practical 10 – Analysis of Abnormal Constituents in Urine
3
1st Term
FOUNDATION MODULE
4
Practical - 1
INTRODUCTION TO LABORATORY
A. Safety in the laboratory.
B. Commonly used laboratory equipment and their applications.
A. SAFETY IN THE LABORATORY
When you work in a laboratory, you may be exposed to many accidents and hazards,
which may occur due to specimens (urine/serum), chemicals/reagents, glassware,
electricity/gasses, equipment etc.
Laboratory Safety Procedures:
1. Each student should take special care about personal hygiene.






Always wear protective clothing (e.g. over (lab) coats, gloves, goggles etc.)
when necessary.
Eating, drinking, smoking, and orating in the lab are hazardous.
Biting fingernails should be strictly avoided.
Any wound, abrasions etc. should be dressed well before entering the lab.
Should not enter the lab with loose hair, high-heeled shoes and fancy dresses and
hanging accessories.
Wash your hands well before leaving the lab.
2. Learn the correct handling of pipettes and never mouth pipette (use fillers/ bulbs)
and consider that all biological materials are hazardous.
3. If any corrosive or infectious materials get spilled on bench, floor or on your
clothes, call a demonstrator or a technician.
4. If anything is splashed on your eyes, quickly wash the eye with running tap
water and report. Always keep the tubes away from the body when
boiling/heating.
5. Do not use any broken glassware or handle them with greatest care. Report any
breakages to the lab staff.
6. When using reagents, read the label carefully and do not move the bottles or
waste and contaminate the reagents. Take care when opening them as some may
exude toxic fumes (e.g. strong acids, NH3 etc.) and close them once used.
7. Do not exceed the specified speed of centrifuges. Allow centrifuge to slow
naturally and wait at least 2 min before opening to prevent contamination
through aerosols.
8. Always switch off the microscope when not in use and never change the field.
9. If there is any fire inside the lab, take actions to stop them. Eg. use sand
baskets/buckets, fire extinguishers, etc.
10. Once you finish working,
 Turn off the gas burner.
 Wash the glassware used and clean the working bench and sink.
 Discard the specimens collected by your selves only (e.g. urine).
5
B. COMMONLY USED LABORATORY EQUIPMENT AND THEIR
APPLICATIONS
Identification and Usage
1. Bunsen Burners
– to heat or boil solutions in containers
2. Clamp and Holders – to hold the glassware in a secure manner
3. Porcelain dishes
– to evaporate solutions
4. Watch glasses
– weigh small quantities
5. Spatulas
– to ease the handing of small amount of substances
6. Stirring rods
– to mix and make homogeneous solution
7. Water baths
8. Urinometer
– incubate samples at a desired temperature in-vitro
e.g. enzyme reactions at 37 C.
– to measure the specific gravity of urine
9. Pipette filler
- to pipette solutions in and out of the pipettes
10. Filters
(i) Filter papers
– to filter solutions
(ii) Muslin cloth
– to filter solution of great impurities
11. Measuring equipment
(i) Micropipettes
(ii) Pasteur pipettes
(iii) Graduated pipettes
(iv) Burettes
(v) Measuring Cylinders
(vi) Beakers
– to transfer very small quantities of liquids
accurately.
Commonly used for serological samples.
– to transfer solution into another glassware
such as measuring cylinder or volumetric flask.
– to transfer a fixed amount of small volumes
Eg 1mL, 2mL, 5mL, 10mL.
– to transfer varying quantity of solution.
Eg in titration
– to measure volumes in larger quantities
Eg 10 mL, 100 mL.
– to measure very large amount of solutions.
Eg 250 mL, 500mL, 1 L, 2L, are available
6
12. pH Measurement
(i) pH papers (universal/litmus) - to measure an approximate pH
(ii) Lovibond comparator
- to measure pH of a solution by comparison
(Eg. urine)
(iii) pH meter
- to measure pH accurately
13. Electrophoretic apparatus
Used to separate molecules according to the charge / molecular mass ratio (e/m).
E.g. paper / gel electrophoretic apparatus
14. Weighing scale
(i) Electrical weighing scale – to measure substances in gram quantity
(ii) Analytical weighing scale – to measure very small amount (Eg g/mg)
15. Absorbance measurements
(i) Colourimeter
Uses colour filters with fixed wavelengths to measure absorbance of a
coloured solution in the visual spectrum.
(ii) Spectrophotometer
Uses a specific wavelength to measure the absorbance of the solution. It
can measure absorbance in the visual as well as in the ultra violet range,
depending on the instrument.
7
Practical - 2
CELL, pH AND BUFFERS
1. pH
All biochemical reactions in the body take place in an aqueous environment and most of
these reactions are catalyzed by enzymes. Enzymes are optimally active at a particular
H+ ion concentration.
Concept of pH
 H+ + Cl-
HCl
Strong acids dissociate to a greater extent and liberate more hydrogen than a weaker
acid. H+ ions can be expressed as mol/L. But a more convenient way to express H+
concentration is in terms of pH.

pH: pH is a measure of the concentration of hydrogen ions (H+ /protons)in a
solution.
Numerically it is the negative logarithm of that concentration expressed in
moles per liter (M).
pH = - log [H+] = log 1
[H+]
From the definition: the higher the hydrogen ion concentration the lower the pH and
vice versa.
Water even in its purest form is weakly ionized as follows.
H2O  H+ + OHAccording to the law of Mass Action,
K (dissociation constant) =
[H+] [OH-]
[H2O]
Since H2O is large and remains practically unaltered.
[H+][OH-] = Constant
Kw
Kw is referred to as the ionic product of water
Kw = 10-14 at 25C (from conductivity measurements)
At neutrality [H+] = [OH-]
Then [H+] 2 = 10-14 [H+]= 10-7 (it is assumed that activities of ions are approximately
equal to their concentration in dilute solution).
When pH < 7, the solution is said to be acidic
PH > 7, that solution is said to be alkaline.
8
1 x 10-14
Concentration of
OH- (moles/liter)
pH
Concentration of
H+ (moles/liter)
1 x 10-7
0
1x 100
7
1 x 100
14
1 x 10-7
(as in pure water)
1x10-14
2. INDICATORS
Indicators change their colours with a change in the pH of the solution containing
them. They are weak acids or weak bases. Their ionized and unionized forms have
different colours. The actual colour in a solution therefore, depends on the ratio of
these two forms. This ratio in turn depends on the pH of the solution containing the
indicator.
2.1 Natural indicators
1. Take 1 mL of 0.1 M HCL and 1 mL of 0.1 M NaOH into two separate test tubes
and add 1 drop of red cabbage juice to each tube and observe the colour change.
Some useful indicators
Indicator
pH Range
Thymol blue (acid range)
Methyl orange
Bromophenol blue
Congo red
Bromo cresol green
Methyl red
Bromo cresol purple
Litmus
Bromothymol blue
Phenol red
Cresol red
Thymol blue (alkaline range)
Phenolphthalein
1.2-2.8
3.1-4.4
3.0-4.6
3.0-5.0
3.6-5.2
4.3-6.1
5.0-7.6
5.0-8.0
6.0-7.6
6.7-8.3
7.2-8.8
8.0-9.6
8.2-10.0
Colour change
Red
Red
Yellow
Violet
Yellow
Red
Yellow
Red
Yellow
Yellow
Yellow
Yellow
Colourless
Yellow
Orange
Purple
Red-Orange
Blue
Yellow
Purple
Blue
Blue
Red
Violet
Blue
Pink
9
3. MEASUREMENT OF pH
3.1. pH papers
Determine the pH of the solutions A and B, tap water and urine using pH papers
provided.
Question:

What is the disadvantage in using pH paper to measure the pH of urine?
3.2. Lovibond Comparator – Demonstration
To 10 ml sample add 0.5ml of appropriate indicator solution.
For the range of pH 4.4 – 6.0 use methyl red
For the range pH 6.0 – 7.6 use Bromo thymol blue
For the range of pH 6.8 – 8.4 use phenol red.
a) The blank contains the same volume of sample without the indicator.
b) The tubes are placed in the Lovibond comparator in such a manner that a
window of the disc covers the blank.
c) The disc is rotated so that the colour on the disc matches with the colour in the
test tube.
d) The corresponding pH is read from the disc. This method is superior to the
previous method as the pH of coloured solution (such as urine) can be estimated
without dilution.
3.3. Electrometric method (pH meter) – Demonstration
4. BUFFERS
Most biological systems will function only within a narrow range of pH and their
activities vary widely within that range. The most important way that the pH of the
blood, urine, extra cellular fluid is kept relatively constant is by buffers dissolved in the
body fluid.
A buffer is a mixture of a weak acid and its conjugate base (respective salt) that resists
change in pH on the addition of small amounts of acids or bases.
How do buffer solutions work?
A buffer solution has to contain ions, which will remove any hydrogen ions or
hydroxide ions that you might add to it – otherwise the pH will change.
The pH of a buffer solution is determined by the ratio of concentration of the acid to its
salt and pK1 value of the acid (pK1a).
It is expressed in the Henderson – Hasselbalch equation.
10
Where
pKa = -log Ka
pH= Pka + log [Salt]
[Acid] of th
(Ka = dissociation constant
A buffer has maximum buffering capacity, when [Salt] = 1
[Acid]
i.e.
pH = pKa + log 1
pH = pKa
The effective buffering range is pH = pKa ±1
4.1. Physiological buffering action of serum
a) Take 1 ml of serum and 1ml of tap water to two separate test tubes.
b) Add a drop of phenol red indicator (pH 6.7 – 8.3) to each tube.
c) Then add 0.01 N NaOH to the tube containing water. Counting the number of
drops you add until the colour change.
d) Then add the same number of drops of 0.01M NaOH to the tube containing
serum and observe whether there is any colour change.
e) Then add another few drops of 0.01 M NaOH to the same serum tube and
observe for any colour change upon adding few drops.

Repeat the same procedure with serum and water with 0.01 M HCl.
Questions:

What is a physiological buffer?

Why did not the serum sample give a colour change even after adding the same
number of acid / base drops to that tube?
5. CHANGES IN CELL MEMBRANE INTEGRITY WITH DIFFERENT
SOLVENTS
a) Take 3 ml of each of following solutions to separate test tubes.
a) Buffer – pH 7.4
b) H2O
c) 0.1 M NaOH
d) 0.1 M HCl
b) Wash the beet root pieces until the red colour is no more.
c) Then put a piece of beet root to each tube and observe the tubes after 10-15
minutes.
d) Record your observations and explain the changes.
11
Exercises
1. Calculate the [H+] when
(a) pH = 4
(b) pH = 2.4
(c) pH = 4.4
2. What is the pH value of 0.001 N HCl acid (assume complete dissociation)
3. Calculate pH when,
(a) [H+] = 10-6
(b) [H+] = 4.3 x 10-8 (c) [H+] = 3.2 x 10-10
4. You are given a weak acid HA (pKa = 5.00) using a log table calculate the pH of
the solution.
% Neutralization
Eg.
1
10
20
30
50
70
80
90
99
99.9
[A-]
[HA]
1/99
…….
…….
…….
…….
…….
…….
…….
…….
…….
log [A-]
[HA]
-2.00
…….
…….
…….
…….
…….
…….
…….
…….
…….
pH
3.00
…….
…….
…….
…….
…….
…….
…….
…….
…….
a) When half the amount of acid has been neutralized what is the pH of the solution?
b) Is this value in anyway related to the pKa of the acid?
c) If you are given indicators Bromo Cresol Green (pKa = 4.7) and Phenol Red
(pK = 7.9) which would you choose to determine the pH at
(i) Half neutralization
(ii) Complete neutralization
d) When this acid is almost completely neutralized what is the pH of the solution?
5. Using the Henderson Hasselbalch equation, calculate the pH values of the
following mixtures (Pka of acetic acid is 4.74)
a) 22mL of 0.1 M CH3COOH + 78mL of 0.1 M CH3COONa
b) 37mL of 0.1 M CH3COOH + 63mL of 0.1 M CH3COONa
c) 85mL of 0.1 M CH3COOH + 15mL of 0.1 M CH3COONa
12
Practical - 3
TESTS FOR CARBOHYDRATES AND LIPIDS
1) TESTS FOR SUGARS
Reduction of copper salts: When cupric hydroxide in alkaline solution is heated it is
converted to cupric oxide. If a reducing sugar is present, the cupric oxide is reduced to
cuprous oxide.
1.1 Benedict’s Test
Perform with glucose, sucrose and maltose. To 5.0mL Benedict’s reagent add 8 drops of
sugar solution and mix. Boil for 2 min. over a flame (or 5 min in a boiling water bath).
Allow to cool. Note the colour of the solution during heating and the colour of the
precipitate, if any.
1.2 Barfoed’s Test
Perform with glucose and maltose. Add 1mL of the sugar solution to 3mL of freshly
prepared Barfoed’s reagent. Mix and place the tube in a boiling water bath and boil for 1
min. Allow the tube to stand at room temperature for 5 min.
Barfoed’s reagent contains copper acetate in acetic acid. Only monosaccharides will
answer this test. Disaccharides may answer the test if boiled for a longer time.
1.3 Seliwanoff’s Test
Perform with solutions of fructose and Glucose. To 10 drops of solution add 5mL of
Seliwanoff’s reagent and heat for 30 seconds (until it boils). Cherry red colour
indicates the presence of fructose.
1.4 Tests for polysaccharides
(a)
Add one drop of dilute solution of iodine to a 6mL of starch solution. Note the
colour produced. Divide the mixture into 3 parts. To one part, add one drop of
dilute HCl. To the second part, add one drop of dilute NaOH. Heat the third
portion gently over a flame. Record your observations.
(b)
Warm a starch solution with dilute HCl. Every minute take a drop of the solution
and add to a drop of iodine solution on a white marble. Note the time at which
solution does not give a colour with iodine. Perform Benedict’s test with the
solution. (Not Done)
Questions:

Explain how you would distinguish 2 unknown solutions, one containing glucose
and the other containing fructose?

State the main difference in the principle of Benedict’s and Barfoed’s tests?
13
Summary of the test for carbohydrates.
Fructose
Galactose
Pentose
Maltose
Lactose
Sucrose
Starch
Dextrin
Glycogen
Benedict’s Test
Barfoed’s Test
Seliwanoff’s
Test
Iodine Test
Glucose
Test
+
+
-
+
+
+
+
+
-
+
+
-
+
-
+
-
-
-
-
-
-
-
-
-
-
-
-
+
+
+
2) TESTS FOR LIPIDS
2.1. Presence of glycerol: (triacylglycerol, phospholipids)
2.1.1 Acrolein Test
Place 1 g solid KHSO4 in a dry test tube and add 2 drops of glycerol. Heat slowly at
first and then vigorously. Note the smell of acrolein. Repeat the test using 8 drops of
coconut oil in place of glycerol.
2.1.2 Rancidity
Test (a) rancid coconut oil (b) fresh coconut oil with litmus paper and with 1 drop of
methyl red indicator.
Record your observation.
Questions:

How does oil become rancid?

What steps could you take to prevent oil and fats becoming rancid?
2.2 Unsaturation of fats and oils
2.2.1 Iodine absorption
Dissolve about 0.1 g fat in 5mL CHCl3. Add Hubl’s iodine solution drop wise,
shaking the tube with each addition. Continue until the iodine colour persists. Count
the number of drops of iodine solution that you had to add before the colour
appeared. Compare with a control tube containing only 5mL of CHCl3 and one
drop of iodine without the lipid.
Carry out this test with
a) Coconut oil
c) Sesame oil
e) Margarine
b) Butter
d) Soya oil
14
2.3 Saturation of oils (demonstration)
Perform with coconut oil and sesame oil. Take 2mL of the above in to two test tubes and
keep in the refrigerator for two hours. Comment on your observation and distinguish
between the saturated and unsaturated.
2.4 Test for phospholipids
2.4.1 Lecithin
(a) Note its smell
(b) Note its solubility in
(i)
Water – only polar part dissolves
(ii)
Acetone – only non polar part dissolves
(iii)
Chloroform – methanol mixture (4:1v/v)
(c) You are provided with a hydrolysate of lecithin in 40% KOH.
(i)
Note the smell of hydrolysate
Acidify 2mL hydrolysate lecithin with 2mL con. HNO3 drop wisely.
Add excess ammonium molybdate (3mL) and heat over a flame
gently. A yellow precipitate indicates the presence of phosphate.
(ii)
Perform the acrolein test with hydrolysate.
2.4.2 Test for cholesterol
(a)
Dissolve about 5mg cholesterol in 5mL alcohol-ether mixture (1:1). Place a drop
of the solution on a slide and examine the crystal (demonstration).
(b)
Liberman – Burchard test (use dry test tube)
Add 10 drops of acetic anhydride and 2 drops of con. H2SO4 to 2mL of a
solution of cholesterol in CHCl3. Note the changes in colour (red to blue to
bluish green).
Questions:

What is the relationship between lecithin and respiratory distress syndrome
(RDS)?

What foods contain high amounts of cholesterol?

Explain the amphipathic nature of cholesterol.
15
Practical - 4
TESTS FOR AMINO ACIDS AND PROTEINS
Physical properties of protein
Precipitation of proteins: Proteins can be precipitated by various methods.
(i)
(ii)
(iii)
(iv)
(v)
(vi)
Neutralization of the charges of protein and subsequent dehydration
Proteins may be precipitated by heavy metals: e.g. Zinc proteinate by Zinc
Sulphate, protein tungstate by tungstic acid etc.
Dehydration, denaturation : e.g. alcohol
Flocculation and coagulation
Isoelectric pH
Precipitation by neutral salts: e.g. (NH4)2SO4
1) PRECIPITATION BY SALTS (Dehydration)
i) To 5 mL of protein solution add an equal amount of saturated (NH4)2SO4 solution.
The ovoglobulin is precipitated. This test is referred to as the half saturation test.
ii) Filter the precipitate
iii) To the filtrate add solid ammonium sulphate and saturate it. Ovalbumin is
precipitated. This is called the full saturation test.
Know the principle behind:
Albumin being more hydrated than globulin requires more salt for dehydration. Serum
albumin and globulin may be separated in this manner.
2) PRECIPITATION BY HEAVY METALS
To 3mL of protein solution, add 5% lead acetate drop by drop and observe the protein
being precipitated. Add more lead acetate. Observe & record your observations. Repeat
the experiment with a solution of AgNO3. Observe the difference.
3) PRECIPITATION BY ACIDS
To 3mL protein solution add a few drops of 20% sulphosalycilic acid. The protein is
precipitated .Repeat the experiment with 1% picric acid and 10% trichloroacetic acid.
4) PRECIPITATION BY ALCOHOL
To 3mL protein solution add 3mL of absolute alcohol. Precipitation occurs. The
mechanism of precipitation in this method is by dehydration, denaturation and removal
of charges.
16
Note: However, if the electrolyte (NaCl) used in dissolving the protein is removed by
dialysis, alcohol is not capable of precipitating the protein.
5) CHEMICAL PROPERTIES: COLOUR REACTIONS
5.1. Test for amino acids (Ninhydrin Test)
To 1mL of amino acid solution add 4-5 drops of ninhydrin in alcohol and boil for
one minute. Development of blue colour indicates the presence of amino acid in
the solution.
5.2. Test for peptide bonds (Biuret Test)
To 3mL protein solution add an equal amount of 5% NaOH and then 4 drops
of 1% copper sulphate. Mix. A purple (pinkish) colour is produced.
5.3. Test for protein (Xanthoprotein test)
To 3mL protein solution, add 2 mL Conc. HNO3. Boil and cool. What is your
observation?
5.4. Test for proteins (Heller’s test)
Place 2mL of concentrated HNO3 in a test tube and incline the test tube. Run a
protein solution down the wall of the test tube until it forms a layer over the
HNO3. Note the protein precipitate at the junction between the two liquids.
5.5. Identify the samples
You are provided with 3 different solutions containing an Amino acid, Peptide &
Protein (A, B & C). Using above tests try to identify the contents in each test tube.
SUMMARY CHART
Test / Experiment
Ninhydrin Test
Biuret Test
Sulphosalicylic acid
Trichloroacetic acid
Picric acid
Hellers Test
Amino acids
+
-
Polypeptides
+
-
Proteins
+
+
+
+
+
17
6) ISOELECTRIC PRECIPITATION
What effect on (a) the charge and
(b) the solubility of a protein would you expect if the pH of the
protein solution is altered?
Steps to follow:
a) To 1.0mL of alkaline casein solution add 0.1 M HCl drop by drop until
maximum precipitation occurs.
b) Check the pH using pH papers
c) Continue the addition of HCl, shaking the tube after each addition, until
the precipitate dissolves.
d) At this point add 0.1 M NaOH drop wise until casein precipitates
e) Continue the addition of NaOH until precipitate redissolves.
f) Record your observations
Resources provided:
Casein solution (1%) w/v)
HCl (0.1 M)
NaOH (0.1M)
HCl (0.05M)
Universal indicator paper
Bromocresol green indicator (pH range ≤4.0 yellow≥ 5.6 blue)
Questions:

What is the biochemical basis of giving egg white in heavy metal poisoning?

What is the purpose of using ZnSO4 when assaying some serum parameters?
18
Practical - 5
ENZYMOLOGY I
Using salivary amylase, investigate the effects of,
1. Substrate concentration
2. pH
3. Temperature
4. Activators and inhibitors
Starch
(Iodine test)
Salivary
amylase
Dextrins / Maltose
The rate of the reaction  rate of disappearance of substrate / min (iodine test)
 rate of appearance of product / min (Benedicts test)
Collection of dilute saliva
Wash the mouth with some water. Then take 10mL warm distilled water into mouth and
move it for about 2 min. Collect fluid into a clean beaker. Filter if necessary.
1) FINDING THE ACHROMIC POINT
Setup two tubes containing
A. 3mL dilute saliva
B. 3mL dilute saliva, boiled for 10 min, and cooled.
Steps to follow:
a) To each tube add 3mL of 1% starch solution.
b) Immediately remove a drop from each tube with a glass rod and test with iodine.
c) Place tubes in a water bath at about 37 C. Remove drops from each tube at 30
second intervals and test with iodine.
d) Observe the colour change from blue to violet, to red and finally becomes
colourless. This is the “Achromic point”. Note the time taken to reach the
achromic point.
Note 1: If the amylase is very active, the achromic point may be observed in a minute
or two. If this happens, dilute the saliva (about 1:10) and repeat.
Note 2: Obtain the saliva that has the achromic point at about 5-8 min.
** Use this dilution of saliva for the tests that follow.
19
2) EFFECT OF SUBSTRATE CONCENTRATION
Dilute the 1% starch solution to obtain 0.8%, 0.4% and 0.2% solutions. To 0.5mL
diluted starch solution, add 0.5mL diluted saliva and 0.5mL buffer (pH 6.0). Incubate at
about 37 C for 5min. Perform iodine test & Benedict’s test with the mixture. Compare
precipitate obtained with each dilution of starch solution. Comment.
3) EFFECT OF pH
To 3 tubes add 1mL phosphate buffer, pH 5.8, 6.6 and 8.0. To each tube add 2mL of 1%
starch solution and 0.5mL diluted saliva. Incubate at 37 C. Determine the time taken by
contents of each tube to reach the achromic point.

What is the optimum pH of salivary amylase?
4) EFFECT OF TEMPERATURE
Using the buffer of optimum pH (determined in above experiment) add 2mL 1% starch
solution and 0.5mL diluted saliva into 3 labeled test tubes. Place one tube in ice (about 4
C). Keep the other 2 tubes, at 20 C, 37 C. Comment on the optimal temperature.
Demonstration:
Cut the potato / apple into two small equal pieces (1/2 inch) and keep one piece open to
air and immerse the other piece in hot water (40 C – 60 C) and keep there for 1-2 mins
(blanching) and take the potato/ apple out and keep it open to the air. Comment on your
observation.
Blanching
- is a term that describes a process of food preparation wherein the food substance,
usually a vegetable or fruit, is plunged into boiling water (enzyme denaturation),
removed after a brief, timed interval and finally plunged into iced water or placed under
cold running water (shocked) to halt the cooking process.
(Ex: tinned fruits and vegetables)
5) EFFECTS OF ACTIVATORS AND INHIBITORS
To 4 tubes, add 2mL of 1% starch solution and 0.5mL of dialysed saliva. Add 2 drops
of 0.1M NaCl, 0.1 M Na2SO4 and mercuric sulphate solution, into each of the 3 tubes.
The 4th one is the control. Test with iodine solution the contents of each of the 4 tubes
after incubating for 5 mins. Comment on your observations.
20
Practical - 6
ENZYMOLOGY II
Introduction
The substrate fibrin is an insoluble clot protein. The dye Congo red (indicator) is
coupled to fibrin. When a protease hydrolyses the protein fibrin, the dye is released into
the solution.
Congo red : Blue < pH 4 < Red
1) ACTIVITY OF TRYPSIN – USING CONGO RED FIBRIN AS SUBSTRATE
a) Set up 5 test tubes as follows.
Tube No.
1
2
3
4
5
Enzyme
2mL Trypsin
2mL Trypsin
2mL Trypsin
2mL Trypsin (boiled and cooled)
2mL H2O
Add
2mL of 0.1M HCl
2mL H2O
2mL 0.05M Na2CO3
2mL 0.05M Na2CO3
2mL 0.05M Na2CO3
b) To each tube add a shred of Congo red fibrin and incubate the tubes in a bath at 37
0
C for 30 min.
c) Explain the observations you make on each tube.
2) EFFECT OF pH ON ACTIVITY OF PEPSIN
a) Set up 6 tubes as follows.
b)
Tube 1 & 2
0.4% HCl
3mL
Distilled water
(pH of the medium) 1.3
c)
d)
e)
f)
Tube 3 & 4
1mL
2mL
1.8
Tube 5 & 6
4 drops
3mL
2.51
Add to each tube a shred of Congo red fibrin.
To tube 1, 3 and 5 add 1mL of 0.5% pepsin solution.
Incubate at 370C for 30 mins.
Comment on your observations.
21
3) OPTIMUM pH FOR TRYPSIN ACTIVITY (Demonstration)
a) Set up tubes as follows;
Tubes
1 and 6
2 and 7
3 and 8
4 and 9
5 and 10
Solution
Approximate pH
1mL water
7
1mL 0.5% Na2CO3
8
1mL 10% Na2CO3
9
1mL 2 % Boric acid
5
1mL 0.4% HCl
1
b) Add a shred of Congo red fibrin to each tube.
c) To tubes 1 -5 add 1mL 0.5% trypsin solution.
d) To tubes 6 – 10 add 1mL of 0.5% boiled and cooled trypsin solution.
 Explain your observations.
 What is the optimum pH for trypsin?
4) EFFECT OF TEMPERATURE ON PEPSIN ACTIVITY (Demonstration)
a) Set up tubes as follows;
Solution
Tube A
Tube B
Coagulated egg white
5mL
5mL
0.8% HCL
5mL
5mL
0.5% Pepsin solution
2mL
0
0.5% Pepsin solution
0
2mL
(boiled and cooled)
Incubate at 37˚C for 30 minutes .compare the 2 tubes and explain observation.
5) CLOTTING OF MILK (Demonstration)
a) Set up tubes as follows;
Solution
Tube 1
Tube 2
Tube 3
Tube 4
Milk
CaCl2 solution
Acetate buffer, pH 5
Pepsin solution
Pepsin solution
(boiled & cooled)
Trypsin solution
Trypsin solution
(boiled & cooled)
5mL
1 drop
5mL
1mL
5mL
1 drop
5mL
-
5mL
1 drop
5mL
-
5mL
1 drop
5mL
-
-
1mL
-
1mL
-
-
-
-
1mL
b) Incubate the tubes at 37 C for 5 min.
c) Explain your observations.
22
6) PRODUCTS OF PEPSIN AND TRYPSIN DIGESTION
Solutions of casein in water (0.5% w/v) digested with
- 1% Pepsin solution at pH 1.3 (sample A)
- 1% Trypsin solution at pH 8 (sample B)
for four days have been provided.
Steps as follows:
a)
b)
c)
d)
e)
f)
g)
Take 25mL of sample A, B in boiling tubes and boil.
Saturate with (NH4)2SO4 crystals.
Filter the precipitates.
Boil the filtrate with an equal volume of 0.5% BaCO3 and filter the BaSO4.
Divide the filtrate in to 3 portions.
Dissolve the precipitate from step 3 in water and divide in to 3 portions.
Test each portion obtained in step 5 & 6 with
(i)
Ninhydrin
(ii)
Biuret reagent
(iii) 10% Trichloroacetic acid
Questions:

Comment on your observation.

What are the products of peptic and tryptic digestion?

By means of equation indicate the difference between the actions of the two
enzymes.

State the differences between an endopeptidase and an exopeptidase.
23
3rd Term
METABOLISM, ENDOCRINE AND NUTRITION MODULE
AND
GASTRO-INTESTINAL TRACT MODULE
24
Guided Learning Session - 1
INTRODUCTION TO CARBOHYDRATES AND LIPID
METABOLISM
Disorders of Carbohydrate Metabolism:
 Defects in Fructose metabolism
 Galactosaemia
 Glycogen storage diseases
 Glucose 6- Phosphate Dehydrogenase (G6PD) Deficiency
 Lactose intolerance
Disorders in Lipid Metabolism:
 Disorders of fatty acid oxidation
 Obesity
o Factors Associated with obesity
o Body Mass Index
 Atherosclerosis
o Steps in the formation of atherosclerotic plaque
o Risk factors for atherosclerosis
25
Guided Learning Session - 2
CATABOLISM AND EXCRETION OF NITROGENOUS
COMPOUNDS
Catabolism and excretion of haem
 Haem metabolism
 Major causes of Jaundice
o Hepatic causes
o Pre – hepatic causes
o Post – hepatic causes
 Reasons for investigating for Neonatal jaundice
 Causes of un-conjugated hyperbilirubinaemia in new born
 Van den Bergh test – Direct and Indirect tests for conjugated and
total bilirubin (principle)
Purine nucleotide metabolism and uric acid synthesis
 Major
inherited
metabolic
diseases
associated
with
hyperuricaemia and development of gout
Metabolism and excretion of creatinine
 Increased creatinine - report
 Biochemical test for Creatinine in urine– Jaffe’s test
Metabolism and excretion of urea
 Disorders associated with urea cycle
 Biochemical test for urea in urine
26
Fixed Learning Module
THYROID HORMONES
At the end of the FLM the student should be able to identify and list the main
features of
 Maternal thyroid function during pregnancy
 Foetus and thyroid gland
 Thyroid deficiency and foetal development
o Isolated maternal hypothyroidism
o Isolated foetal hypothyroidism
o Combined maternal and foetal hypothyroidism (iodine deficiency)
 Role of thyroid hormones in brain development
 Hyperthyroidism in pregnancy
 Fasting and thyroid hormones
 Tests to measure serum thyroid hormones
27
Guided Learning Session - 3
DIABETES MELLITUS
Formation of Advanced Glycation End Products (AGE s)
Biochemical mechanisms of development of long term diabetic complications

Eye and eye sight
o Diabetic retinopathy
o Diabetic cataract

Diabetic nephropathy

Diabetic neuropathy

Micro - angiopathy in diabetes mellitus
Formation and structure of Fructosamine
Formation and structure of Haemoglobin A1c

Determination of HbA1c in the laboratory (principle and methods)
Tests for diabetes mellitus (methods and graphs)

Glucose Challenge Test (GCT)

Oral Glucose Tolerance Test (OGTT)
Patterns of OGTT curves

Normal GTT curve

GTT curve in severe diabetes mellitus

GTT curve in mild diabetes mellitus

Flat GTT curve

Lag curve

Curve in renal glucosuria
28
Practical - 7
DETERMINATION OF GLUCOSE IN URINE AND SERUM
Note: Every test should be compared with a normal urine sample (control). Note the
colour, smell, and nature of any deposit or any turbidity before testing.
1. Test for reducing substances in urine
Reducing substances present in abnormal urine could be
a. Reducing sugars : hexoses, pentoses
b. Other substances : Vitamin C, homogenistic acid, salicylic acid
1.1 Benedict’s test (Preliminary test for screening for reducing substances in urine)
To 2.5 mL of Benedict’s reagent, add 4 drops of abnormal urine. Boil for 2 min over a
flame or place the tube in a boiling water bath for 5 min. Allow to cool slowly.
Observe the colour of the precipitate and colour of the supernatant.
Colour of Precipitate
Colour of Solution
No precipitate
Blue
with
Approximate Strength
green 0.1%
opalescence
Slight yellow precipitate
Blue on standing
0.2%
Slight orange precipitate
Green (Blue on standing)
0.3%
Definite orange precipitate
Green (Blue on standing)
0.5%
Deep orange precipitate
Green (Blue on standing)
1.0%
Bright red precipitate
Blue
colour
almost 2.0%
disappears
Questions:

What is the basis of Benedict’s test?

What are the simple sugars that will answer for Benedict’s test?
1.2 Seliwanoff’s resorcinol test (Confirmatory test for the presence of fructose)
To 5mL of Seliwanoff’s reagent, add 10 drops of urine and heat for 30 seconds. Cherry
red colour indicates the presence of fructose.
29
1.3 Clinistix strip test (Confirmatory test for the presence of glucose)
Dip the test strip in urine sample. Remove excess urine by touching the side of the
container. Compare the colour developed with the given colour chart in the bottle (read
the instructions).
Theory:
Glucose
O2
Glucose oxidase
Gluconic acid
H2O2
Chromogen
Peroxidase
H2O
Oxidized chromogen
Note: Colour appearing after 2 minutes, does not have any significance.
Questions:

What are the substances impregnated in the strip?

Why is Clinistix strip test specific for glucose?
2. Determination of glucose in serum
The same principle applied to the clinistix test is used in the reagent kit for the
determination of glucose in serum. Here, the colour intensity of the solution in
measured at 500 nm. The absorbance is directly proportional to the amount of glucose
present in the sample.
Method
Pipette in to labeled test tubes
Blank
Standard Test
Reagent
1 mL
1 mL
1 mL
Demineralized water
10 μL
-
-
Standard
-
10 μL
-
Serum
-
-
10 μL
Incubate for 10 min at 37oC and measure the absorbance in the spectrophotometer
(Shimadzu – UV 200, Japan), at 500 nm.
30
Guided Learning Session - 4
INTRODUCTION TO ENDOCRINE DISORDERS
Hypothyroidism
 Causes and clinical features of hypothyroidism
 Biochemical basis for the features
 Iodine and goitre
 Congenital hypothyroidism (cretinism)
o Causes and clinical features of cretinism
Hyperthyroidism
 Causes and clinical features
Growth hormone
 Acromegaly
 Clinical features of acromegaly
Addison’s disease
 Causes and clinical features
Cushing’s syndrome
 Causes and clinical features
31
Practical - 8
DIET
Food records, calculation of energy requirement and energy intake by using Food
Composition Tables (FCT).
Preparation:
Keep a one day food record of everything you eat and drink, noting the nature of the
food, method of preparation and portion consumed prior to practical day.
 Analyze your food record in terms of nutrients and calorie intake in
comparison with the RDA’s (Recommended Daily Allowances).
 Calculate your BMI. Do you see ways of improving your diet?
Note: Students are requested to bring their own calculators.
Reference tables:
Please refer the food guide and food comparison tables to calculate RDA values.
Eg:
Food Comparison Tables of Sri Lanka
Food and Nutrition
(Annexure 1)
– MRI
– T.W.Wickramanayake(Text book)
Food Guide Tables: Points to guide
(A)
One tea cup full of raw provisions (approximate dry weight)
Rice
90g
Pulses
100g
Leafy vegetables
80g
Other vegetables
200g
Coconut (scraped)
25g
Lean meat/ fish
50g
Dried fish
75g
(B)
(C)
Rice
One saucer of boiled rice weight
Uncooked 100g rice weight
100g raw rice
=
=
=
225g
270g of boiled rice
360 kcal
Snack
Cake 1 slice contains 4 teaspoonfuls (tsp) of sugar
Coke (300mL contains 7 tsp sugar)
Biscuit contain ¾ tsp sugar
One tsp (sugar) = 5g (19 kcal)
White sugar contains 387 kcal/ 100g
32
(D)
Food
White bread
Lean meat
Meat
Medium fat
PUFA
Fat
Saturated
Whole milk
Milk
Low fat
Skimmed
Whole egg
Quantity
1 slice (=1/4 inch)
1 oz (28 g)
Protein (g)
3
7
Energy (Kcal)
70
50
1 oz
1 tsp (5mL)
1 tsp (5mL)
7
8
8
8
7
75
45
45
150
120
90
160
240mL = glass
one
33
Practical - 9
ESTIMATION OF LIVER ENZYMES AND CONSTITUENTS OF
BILE
1. Constituents of Bile
1.1 Hay’s test (for bile salts):
Sprinkle a little amount of finely powdered sulphur on the surface of the urine in a tube.
Sulphur powder sinks down in the presence of bile salts and floats on normal urine.
Note: Above test depends on the surface tension reducing property of bile salts.
Question:
 Give one clinical condition where bile salts can appear in urine.
1.2 Fouchet’s test (test for bile pigments):
Slightly acidify 2mL of urine with dil. acetic acid. Add 1mL of 10% BaCl2, mix and
filter. Spread out precipitate on the filter paper and dry over a Bunsen flame or dry by
placing it on a second dry filter paper. Place a drop of Fouchet’s reagent on the
precipitate. Observe the colour. Green colour indicates the presence of bile pigment
(bilirubin).
Note: When an ion chloride in acid solution is added to a precipitate from urine
containing bilirubin green colour is formed.
1.3 Ehrlich’s test (test for the presence of urobilinogen in urine):
Add 8 drops (0.5mL) of Ehrlich’s reagent to 2mL of freshly voided urine. A red colour
indicates the presence of urobilinogen. Warming may intensify the colour.
Note: Normal urine also contains urobilinogen.
2. Estimation of Liver Enzymes
Note: Either method 1 or method 2 will be carried out.
Method 1 - Kinetic method
2.1 Test for Aspartate Transaminase (AST)
Serum AST also known as Glutamic Oxaloacetic Transaminase (GOT) is one of several
enzymes that catalyses the exchange of amino and oxo groups between α-amino acids
and α-oxo(keto) acids. AST is widely distributed throughout the tissues with significant
amounts in the heart and liver (Normal range: 0-20 U/L at 300C).
34
Eg. In myocardial infarction (MI), serum AST may begin to rise within 6-8 h after onset
peak within 2 days, and return to normal by the 4th or 5th day post infarction.
Principle:
AST/GOT
2-Oxoglutarate + L-Aspartate
Glutamate + Oxaloacetate
Malic dehydrogenase
Oxaloacetate + NADH + H+
L-Malate + NAD+
Materials:
AST reagent
Unhaemolized serum samples
Spectrophotometer
Procedure:
1) Set the wave length of the Spectrophotometer at 340 nm.
2) Zero the Spectrophotmeter with deionized water.
3) For each sample dispense 2.0mL of reconstituted AST reagent in to the cuvettes
or test tubes and warm to the reaction temperature (300C).
4) Add 0.2mL of sample to its respective test tube and mix gently. Incubate for 30
seconds at the reaction temperature.
5) Record the decrease in absorbance at 60 seconds intervals (ΔA/ min). The rate of
change should be constant.
6) If the cuvette is not temperature controlled, incubate the samples at the reaction
temperature between readings.
Calculation:
U/L
= ΔA/ min
x
Absorptivity
Total volume (2.2mL)
Sample volume (0.2mL)
Note: The micromolar absorptivity extinction coefficient of NADH is 0.0062 at 340 nm.
2.2 Test for Alanine Aminotransferase (ALT)
Serum GPT (Glutamic Pyruvic Transaminase) is known as ALT. ALT is one of several
enzymes that catalyse the exchange of amino and oxo groups between α-amino acids
and α-oxo acids. ALT is widely distributed in human tissues with the largest amount
found in the liver (Normal range: 0-22 U/L at 300C).
.
35
Principle:
ALT/GPT
2-Oxoglutarate + Alanine
L-Glutamate + Pyruvate
Lactate dehydrogenase
Pyruvate + NADH + H+
Lactate + NAD+
Materials:
ALT reagent
Unhaemolized serum samples
Spectrophotometer
Procedure:
1) Set the wave length of the instrument at 340 nm.
2) Zero with deionized water.
3) For each sample dispense 2.0mL of reconstituted ALT reagent in to the cuvettes
or test tubes and warm to the reaction temperature (300C).
4) Add 0.2mL of sample to its respective test tube and mix gently. Incubate for 30
seconds at the reaction temperature.
5) Record the decrease in absorbance at 60 seconds intervals (ΔA/ min). The rate of
change should be constant.
6) If the cuvette is not temperature controlled, incubate the samples at the reaction
temperature between readings.
Calculation:
U/L =
ΔA/ min
x
Absorptivity
Total volume (2.2mL)
Sample volume (0.2mL)
Note: The micromolar absorptivity extinction coefficient of NADH is 0.0062 at 340 nm.
Method 2 - Colourimetric Method
ALT is present in very high amounts in liver and kidney, and in smaller amounts in skeletal
muscle and heart. Although serum levels of both AST and ALT become elevated when ever
diseases processes affecting liver cell integrity, ALT is the more liver specific enzyme. Elevation
of ALT persists longer than those of AST activity.
AST is distributed in all body tissues, but greatest activity occurs in liver, heart, skeletal muscles
and in erythrocytes. Although serum levels of both AST and ALT become elevated when ever
disease processes affecting liver cell integrity (viral hepatitis, liver necrosis, cirrhosis),occur,
increased AST activity in serum or plasma appears in more than 97% of cases of myocardial
infarction.
36
Principle:
2-Oxoglutarate + L-Aspartate
AST/TGO
Glutamate + Oxaloacetate
ALT/TGP
2-Oxoglutarate + Alanine
L-Glutamate + Pyruvate
Then pyruvate or oxaloacetate reacts with colouration reagent, which absorbance at 505
nm in alkaline solution is proportional to AST or ALT activity in the reactional mixture.
Materials:
Vial R1: AST/TGO substrate
Vial R2: ALT/TGP substrate
Vial R3: Colouration reagent
Vial R4: Standard solution
Procedure:
Table 1: Standard Curves establishment
Let stand reagents and specimens at room temperature.
Pipette into test tubes (mL)
Tube No
1
2
3
4
Demineralized water
0.2
0.2
0.2
0.2
R1 or R2
1
0.9
0.8
0.7
R4 (standard)
0.1
0.2
0.3
R3 (colourant)
1
1
1
1
Mix. Let stand for 20 minutes at room temperature. Add:
NaOH 0.4 N
10
10
10
10
Mix. Let stand 5 minutes and read absorbances at 505 nm against water.
TGO units
0
30
70
135
TGP units
0
40
80
140
There’s no need to plot a new curve at each determination.
5
0.2
0.6
0.4
1
6
0.2
0.5
0.5
1
10
10
225
225
350
325
Table 2:
Let stand reagents and specimens at room temperature.
Pipette into test tubes
Reagent R1
Reagent R2
Incubate for 5 minutes at 37 C. Add:
Serum
Mix and incubate at 37 C during
Reagent R3
TGO
1 mL
-
TGP
1 mL
200 L
Exactly 1hr
1 mL
200 L
Exactly 30 mins
1 mL
37
Mix and let stand 20 minutes at room temperature. Add:
NaOH 0.4 N
10 mL
10 mL
Mix let stand 5 minutes and read absorbances at 505 nm against water.
Note:
Blank reagent: replace serum by demineralized water in table 2.
Calculation:
Plot standard curve on millimeter paper (absorbances) or semi-log (% of transmission)
handling as indicated in table 1.
Abscissa (x axis): Number of units (International Units (IU) / Litre (L))
Ordinate (y axis): Absorbances (or % of transmission)
Transfer “Assay” absorbances or % of transmission on standard curve and calculated
AST or ALT activity in UL/L.
Expected values:
ALT
Newborns, Infants
Men
Women
AST (IU/L)
Newborns
Infants
Adult
At 30C
9 -32
7 - 28
5 - 25
At 30C
25 - 75
15 - 60
8 - 20
At 37C
13- 45
10 - 40
7 - 35
At 37C
39 - 117
23 - 94
13 - 31
38
CASE HISTORY I (From Module Book)
A 20 year old student developed flu like illness with loss of appetite, nausea and pain in
the right hypochondrium. On examination the liver was just palpable and was tender.
Two days later he developed jaundice, his urine became darker and his stools became
pale.
Investigations
On presentation
One week later
Reference range
Bilirubin
38 μ mol/L
230 μ mol/L
3.4 – 22 μ mol/L
Albumin
40 g/L
38 g/L
38 – 55 g/L
AST
450 IU/L
365 IU/L
5 – 35 IU/L
ALP
70 IU/L
150 IU/L
38 – 126 IU/L
GGT
60 IU/L
135 IU/L
8 – 78 IU/L
Bilirubin
positive
positive
Urobilinogen
positive
negative-
Serum
Urine
Comments
The first set of results is characteristic of early hepatitis with raised amino-transferase
reflecting cell damage. This usually precedes the rise in bilirubin and the development
of jaundice.
Impairment of the hepatic secretion of conjugated bilirubin and of
urobilinogen uptake from the portal blood causes both these substances to be excreted in
the urine.
The second set of results show the expected high serum bilirubin but with a fall in AST
as the phase of maximum cellular damage has passed. An increase in ALP, usually of
not more than three times the ULN (Upper Limit of Normal), is common at this stage.
In hepatitis, the bilirubin in plasma is both conjugated and unconjugated, with the
former predominating. Conjugated bilirubin is excreted in the urine and the pale stool
reflects the decreased biliary excretion. The serum bilirubin has remained normal in this
acute illness.
39
CASE HISTORY 2 (From Module Book)
A middle aged female was admitted to hospital following a haematemesis. Endoscopy
revealed the presence of oesophageal varices. The only biochemical abnormality was an
elevated GGT (245 IU). Her varices were treated by sclerotherapy and no further
bleeding occurred. The patient was told to abstain from alcohol. She was admitted one
year later jaundiced, drowsy and with clinical signs of chromic liver disease.
Investigations
Reference range
Serum Albumin 25 g/L
38 – 55 g /L
Bilirubin 260 μ mol/L
3.4 – 22 μ mol/L
ALP 315 IU/ L
38 - 126 IU/ L
AST 134 IU/ L
5 – 35 IU/ L
GGT 360 IU/ L
8 – 78 IU/ L
Comments
The patient had continued to drink and the resulting liver damage eventually affected
hepatic function. The decreased serum albumin, elevated serum bilirubin and enzyme
changes are consistent with cirrhosis and active liver cell damages; the prothrombin time
was also prolonged.
Hepatic decompensation may be precipitated in chronic liver disease by sepsis, bleeding
in to the gut, for example from varices, erosions and ulcers and by various drugs
including diuretics. Diuretics may be given to treat ascites, a common feature of chronic
liver disease, but must be used with caution. The pathogenesis of ascites is complex.
Portal hypertension due to hepatic venous obstruction causes splanchnic arterial
vasodilation. This leads to under filling of the arterial circulation and stimulation of
renal sodium and water retention. Hypoalbuminaemia may also contribute.
(Abstracted from Clinical Biochemistry, William. J. Marshall, 4th Edition)
40
4th Term
Renal Module
41
Practical - 10
ANALYSIS OF ABNORMAL CONSTITUENTS IN URINE
Introduction
Abnormal Urine may contain reducing substances (hexoses, pentoses, vitamin C),
Proteins (albumin, Bence Jones protein), ketone bodies (acetone, aceto acetic acid), bile
salts & bilirubin (bile pigment).
The presence of abnormal constituents in urine is used to diagnose certain diseases.
eg; nephritic syndrome.
Every test should be compared with a normal urine sample (control). The colour, smell
and the nature of any deposit or any turbidity should be noticed before testing.
Storage of urine sample:
Urine should be sampled immediately after collection for best results. If storage is
essential refrigeration or freezing is required to minimize the microbial degradation
followed by acidification.
Urine samples are preserved by different methods depending on the nature of the
analysis attempted.
Eg: Samples are collected under toluene or oil (determination of pH, amylase activity) or
collected in 10% acetic acid solution (estimation of ascorbic acid)
Sometimes, however, estimation of substances (eg: ascorbic acid) is best carried out as
soon as each specimen is voided. All investigations should be conducted on 24 hours
urine samples.
Note:
Preliminary tests are used to screen for the presence of abnormal groups of substances
in urine.
Confirmatory tests will confirm the presence of a particular abnormal constituent.
1. Measurement of specific gravity and total solids
Determine the specific gravity by means of the urinometer. Apply the temperature
correction. viz. Urinometer is calibrated at 20 ˚C. Therefore temperature correction is
necessary. The addition of one unit to the third place of decimals in the reading for every
three degrees centigrade rise of temperature above calibration temperature of the
urinometer and vice versa.
42
Eg:
Reading on urinometer
Room temperature
Temperature correction
Specific gravity
= x
= 32 ˚C
= 32 ˚C -20 ˚C = 4
3
= 1000 + x + (0.001 * 4)
1000
Note: Urinometer should not touch the walls of the container.
Calculate roughly the total solids as follows;
Total solids = 2.66 X (last two figures of the four figured number
expressing specific gravity)
State
importance
of measuring specific gravity
of urine.
Eg: the
If specific
gravity
= 1020,
Total solids
= 2.66 X 20 g/L
Assuming daily excretion
= 1500 mL urine
Total solids
= 2.66 X 20 X 1.5 g/24 hours
2. Tests for reducing substances in urine
Reducing substances present in abnormal urine could be
1. Reducing sugars –
hexoses, pentoses
2. Other substances –
vitamin C, homogentisic acid, salicylic acid.
2.1 Benedict’s test (Preliminary test – to screen for the presence of reducing
substances in urine)
To 2.5 ml of Benedict’s reagent, add 4 drops of abnormal urine. Boil for 2 min over
a flame or place the tube in a boiling water bath for 5 min. Allow to cool slowly.
Observe the colour of the precipitate and colour of the supernatant.
Colour of precipitate
Colour of the solution
Approximate strength
of reducing sugars (%)
0.1
No precipitate
Blue with green opalescence
Slight yellow
Blue on standing
0.2
Slight orange
Green (Blue on standing)
0.3
Definite orange
Green (Blue on standing)
0.5
Deep orange
Green (Blue on standing)
1.0
Brick red
Blue colour almost disappears
2.0
43
Questions:
1. What is the basis of Benedict’s test?
2. What are the simple sugars that will answer for Benedict’s test?
2.2 Seliwanoff’s resorcinol test (confirmatory test for presence of fructose)
To 5ml Seliwanoff’s reagent, add 10 drops of urine and heat for 30 seconds. Cherry
red colour indicates the presence of fructose.
Note: observe the colour of normal urine, abnormal urine (containing fructose only and
glucose only).
Question:
1. Why does glucose also answer for Seliwanoff’s resorcinol test after prolonged
heating?
2.3 Clinistix strip test (confirmatory test for presence of glucose)
Glucose oxidase method:
Dip the test strip in urine sample. Remove excess urine by touching the side of the
container.
Compare the colour developed with the given colour chart in the bottle (read the
instructions)
Glucose
O2
Glucose oxidase
Gluconic
acid
H2O2
Chromogen
Peroxidase
H2O
Oxidised Chromogen
3. Test for proteins
Note: Cells, casts in the urine must be removed by centrifugation before performing
the test for proteins.
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Different types of proteins that can appear in urine:




Albumin
- in nephritic syndrome, diebetic nephropathy
Globulins
Haemoglobin
Bence-Jones proteins
Note: Normal adult urine contains <150 mg of total protein in 24h urine sample. Of this
15-20 mg is albumin.
3.1 Heat precipitation test (Preliminary test)
Fill ¾ of a test tube with the urine sample. Heat the top 1/3 of the urine in the test tube to
boil. Observe the change.
Add 3 drops of 10% acetic acid and observe.
Note:
Any increase in the turbidity in the upper 1/3 compared to the lower unheated part
indicates the presence of proteins and phosphates. When about 3 drops of acetic acid is
added turbidity due to phosphate disappears. If turbidity remains it indicates the
presence of proteins.
Question:
1. What is the basis for turbidity?
3.2 Sulphosalicylic acid test (confirmatory test)
Mix 1ml urine with 2-3 drops of 3% Sulphosalicylic acid. Turbidity indicates the
presence of proteins.
Note: Proteins are precipitated by Sulphosalicylic acid. The degree of turbidity is an
estimation of the quantity of proteins present in the urine sample.
False positive:
 Patients on certain drugs (penicillin, tolbutamide)
 Presence of high concentration of urates in urine.
3.3 Heat coagulation test [Specific test for Bence-Jones protein (BJP)]
Boil 5ml of faintly acidic urine (check the pH). BJP Precipitate at 40o C, maximally at
60 oC. It disappears at 100 oC and reappears on cooling.
Note: Filter the boiling urine rapidly to remove if any albumin present.
Questions:
1. What are Bench-Jones, Proteins (BJP)?
2. Give one clinical condition where BJP can be present in urine?
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3. Ortho–toludine test (test for haemoglobinuria)
Test sample: Boil 2 ml of urine and cool & Control : Take 2 ml of distilled water.
To both tubes add 4 drops of freshly prepared 4% orthotolidine solution in glacial acetic
acid followed of drops of 10% H2O2 solution. A bluish colour will develop. Observe
within two minutes.
4. Test for ketone bodies (acetone , acetoacetic acid)
Ketone bodies are detected in urine of persons suffering from diabetic ketoacidosis and
persons on high fat diets or prolonged starvation.
4.1 Rothera , s test (Preliminary test- acetone , acetoacetic acid both will answer)
Add crystals of ammonium sulphate to 5ml of urine and mix in a test tube until
saturation.
Add 8 drops of 5% sodium nitroprusside solution and mix.
Lay (along the test tube wall) 1ml of conc. ammonia solution without shaking.
A purple ring at the junction of liquids indicates the presence of one or both ketone
bodies.
4.2 Gerhardt’ s test (Confirmatory test)
To 3ml of urine, add 3% FeCl3 solution drop by drop.
Mix while adding.
A brown-red precipitate may form, filter and add 3% FeCl3 continuously to the filtrate
until a colour (purple) appear.
Heat and see whether the colour disappears or not. Purple colour indicates the presence
of acetoacetic acid or salicylates.
On heating purple colour due to acetoacetate disappears, but colour due to salicylates
persist.
Note: salicylates can interfere with the test.
4.3. Ketostix strips
Dip the strip in fresh urine sample.
Remove excess urine by touching the side of the container.
Compare the colour developed with the given colour chart after the given time. (Read
the instruction).
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5. Test for the presence of the pigment/ bile in urine
5.1 Hay’s test (Preliminary test)
Sprinkle little amount of finely powdered sulphur on the surface of the urine in a tube.
Sulphur powder sinks in the presence of bile salts, and floats on normal urine.
Note: above test depends on the Surface tension reducing property of bile salts.
Question:
1. State a clinical condition where bile can appear in urine.
5.2 Fouchet’s test (Test for bile pigment-Confirmatory Test)
Add 1ml of 10% BaCl2 to 2ml of acidified urine.
Mix and filter.
Spread out the precipitate on the filter paper and dry over a Bunsen flame or dry by
placing it on a second dry filter paper.
Place a drop of Fouchet’s reagent on the precipitate.
Observe the colour.
Green colour indicates the presence of bile pigment (bilirubin)
Note: when an ion chloride in acid solution is added to a precipitate from urine
containing bilirubin, green colour is formed.
5.3 Test for Urobilinogen
Questions:
1. What is the purpose of doing the Ehrlich’s test?
2. Is it possible to get a positive response to a normal urine sample?
3. How does Urobilinogen from?
4. List a single method for screening the urine for abnormal constituents?
SCREENING OF URINE FOR THE PRESENCE OF MANY ABNORMAL
CONSTITUENTS - Dipstix method
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Purpose of the test, for use by the public is for screening. Complete diagnosis may
require professional experience and judgment followed by further tests.
The urinary constituents which can be identified: Leucocytes, Nitrite, Uroblinogen,
Protein, pH, Erythrocytes, Hb, Specifc Gravity, Ketones, Bilirubin and Glucose.
Tests are degraded by light. Only remove cap to extract a strip. Replace cap as soon as
possible.
Reference: http://uristik.com/acatalog/URINE_TESTING_INFORMATION.html
Exercise:
You are provided with an abnormal urine sample containing an abnormal constituent.
Confirm the abnormal constituent using the correct preliminary and confirmatory
tests.
Question:
What condition can give rise to the presence of this abnormal constituent in urine?
Further reading: Varley’s Practical Biochemistry.
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