Objectives
Mention the normal serum creatinine level
Enumerate the methods of estimation of
creatinine
Discuss the clinical significance for
increased and decreased serum creatinine
What is Creatinine?
Creatinine (from the Greek ''kreas'', flesh) is
a break-down product of creatine phosphate
in muscle, and is usually produced at a fairly
constant rate by the body (depending on
muscle mass).
Creatinine is a metabolic product of
creatine and phosphocreatine, which are
both found almost exclusively in muscle.
Thus, creatinine production is proportional
to muscle mass and varies little from day
to day.
However, production can change over
periods of time if there is changes in
muscle mass. Age-and gender-associated
differences in creatinine production are
also largely attributable to differences in
muscle mass.
Although diet ordinarily accounts for only a
relatively small proportion of overall
creatinine excretion, it is another source of
variability in serum creatinine levels.
Creatine from ingested meat is converted
to creatinine and can be source of up to
30% of total creatinine excretion.
Thus, variability in meat intake can also
contribute to variability in serum creatinine
levels.
The conversion of creatine to creatinine can
occur with cooking. Since creatinine is readily
absorbed from the gastrointestinal tract,
ingesting cooked meat can lead to a rapid
increase in serum creatinine levels.
Serum creatinine test used to diagnose impaired
renal function. It is more specific and sensitive
indicator of kidney disease than BUN, although
in chronic renal disease, both BUN and
creatinine are ordered to evaluate renal
problems,
because
BUN/creatinine
ratio
provides more information.
A-
Increased Serum Creatinine:
– Impaired renal function.
– Chronic nephritis.
– Muscle disease
B-
Decreased Serum Creatinine
– Decreased muscle mass.
– Advanced and severe liver disease.
– Inadequate dietary protein.
Determination of serum Creatinine
Types of Samples:
Serum or plasma with heparin and urine. Serum or
plasma samples are stable for 24 hours at 2-8o C.
To assay urinary creatinine, dilute the sample 1/20 in
deionized water. Multiply the final result by 20.
Requirements
Requirements:
Automatic pipettes
Tips
Cuvettes
 Spectrophotometer
 Reagent
Specimen:
Serum or plasma
Working Reagent
Mix equal parts of each reagent (A and B) prior to assay.
The concentration in the working reagent are:
Picric acid
55 mM
Sodium carbonate
50 mM
NaOH
0.40 M
Preservative and stabilizers
Preparation of Cuvettes
Blank
(only Reagent)
Standard
(Reagent+ St. sample)
Sample
(Reagent+Serum)
At alkaline pH values, creatinine reacts with picric acid
to produce a coloured compound, creatinine
alkaline picrate, which is photometrically measured.
Reagents
Creatinine Standard (μl)
Serum Sample (μl)
Creatinine Reagent (ml)
1
2
3
200
-
-
-
200
-
2.0
2.0
2.0
Mix well.
Read the absorbance at 546 nm (510 546).
Zero the spectrophotometer against blank.
Read the absorbance after 20 second (A1)
and after 80 second (A2).
Calculate the absorbance change (Δ A).
Calculations:
For Serum:
Serum Creatinine (mg/dl) =
Absorbance of the sample (A2 - A1 ) X Con. Of std
Absorbance of the standard ( A2 - A1 )
Serum creatinine (mg/dl)
Males
Females
0.6 - 1.1
0.5 – 0.9