CC1: CARBOHYDRATES
CARBOHYDRATES (SAS 18-20 & PPT 4)
-
Immediate sources of energy for the body
Provides structural integrity to cell membrane
Determines antigenicity
Extraneous origin
Classified
into
monosaccharides,
disaccharides, polysaccharides
GENERAL DESCRIPTION OF
CARBOHYDRATES
• Carbohydrates are compounds containing C, H,
and O.
• general formula for a carbohydrate is Cx(H₂O)y.
• All carbohydrates contain C=O and –OH functional
groups.
• There are some derivatives from this basic formula
because carbohydrate derivatives can be performed
by the addition of other chemical groups, such as
phosphates, sulfates, and amines.
• GLYCERALDEHYDE is the smallest carbohydrate
and a three-carbon compound
Classification is based on the structure of
carbohydrates.
A. Monosaccharides are simple sugars that contain
four to eight carbons and only one aldehyde or
ketone group. These are reducing sugars (i.e., they
can give up electrons). Examples include glucose
and fructose.
- D-glucose is the most important of all the
simple carbohydrates. D-galactose and D-fructose
are the two other important hexoses.
B. Disaccharides/Oligosaccharides are formed by
the interaction of two monosaccharides with the loss
of a water molecule and are sometimes referred to
as disaccharides. Examples include maltose,
lactose, and sucrose.
- Maltose (2 glucose units)
- Sucrose (glucose and fructose)
- Lactose (glucose and galactose)
C. Polysaccharides are formed by interactions
between many units of simple sugars. Examples are
starch and glycogen.
- Starch, Cellulose, Glycogen, Inulin
(fructose units)
Carbohydrate measurements: important in
diseases that result from abnormal carbohydrate
metabolism such as hypoglycemia and diabetes
mellitus.
Lactase deficiency: lead to lactose intolerance
Deficiency in either galactokinase or galactose
phosphate-1-phosphate uridyl transferase will cause
galactosemia. Screened using the Guthrie test and
Beutler method.
Specimens
used
for
carbohydrate
measurements include whole blood, plasma or
serum. Carbohydrate concentrations in urine, CSF
and other body fluids are also measured in some
conditions that are of clinical importance.
MONTEMAR, T.M.
Metabolic pathways.
• Embden-Meyerhof pathway
• Hexose monophosphate shunt
• Glycogenesis
PATHWAYS IN GLUCOSE METABOLISM
• Gluconeogenesis
• Glycogenolysis
• Glycogenesis
• Lipogenesis
• Lipolysis
HORMONES AFFECTING/REGULATING BLOOD
GLUCOSE LEVELS
• Insulin:
- Only hormone that lowers blood glucose by
inhibiting
glycogenolysis
and
gluconeogenesis in the liver and increasing
glucose uptake by the peripheral tissues;
inhibits release of glucose from the liver
- Produced by the beta cells of the pancreatic
islets of Langerhans
- It is inhibited by the scarcity of dietary fuels
and during periods of trauma due to
increased epinephrine levels
- promotes the entry of glucose into liver,
muscle, and adipose tissue to be stored as
glycogen and fat
- active insulin comes from the cleavage of Cpeptide off the pro-insulin. C-peptide has
become a marker for endogenous production
of insulin to differentiate it from exogenous
insulin. Elevated levels of C-peptide (>1.9
ng/ml; NV is <1.2 ng/ml) suggests
hyperinsulinism characterized by severe
hypoglycemia
- C-peptide to insulin ratio: expected to be 5:1
• Somatostatin:
- Synthesized by delta cells of the pancreatic
islets of Langerhans;
- inhibits secretion of insulin, glucagon, and
growth hormone, resulting in an increase in
plasma glucose level
• Growth hormone and adrenocorticotropic
hormone (ACTH):
- Hormones secreted by the anterior pituitary
that raise blood glucose levels
- Increases blood glucose by inhibiting uptake
of glucose by cells and due to its antagonistic
action on insulin
• Cortisol:
- Increases blood glucose primarily by
stimulating gluconeogenesis by promoting
protein catabolism and deamination and it
inhibits glucose metabolism in peripheral
tissues
- Like the Growth Hormone (GH), it promotes
long-term regulation of blood glucose
- Secreted and produced by the fascicular
cells of the adrenal cortex upon stimulation
by adrenocorticotropic hormone (ACTH)
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CC1: CARBOHYDRATES
-
stimulates glycogenolysis, lipolysis, and
gluconeogenesis
• Epinephrine:
- Increased blood glucose by activating
adenylate cyclase to produce cAMP which
further activates the enzyme phosphorylase
causing increased glycogenolysis
- Like glucagon, it is responsible in the shortterm glucose regulation
- is secreted and produced by the chromaffin
cells of the medulla of the adrenal glands.
- It stimulates glycogenolysis and lipolysis; it
inhibits secretion of insulin.
- Physical or emotional stress causes
increased secretion of epinephrine and an
immediate increase in blood glucose levels.
• Glucagon:
- Together with the hormones epinephrine,
cortisol, and GH oppose many actions of
insulin
- Secreted by the (alpha) α-cells of the
pancreatic islets of Langerhans
- increases blood glucose by stimulating
glycogenolysis and gluconeogenesis in the
liver
• Thyroxine/thyroid hormone:
- increases blood glucose by stimulating
glycogenolysis, accelerating degradation of
insulin, and promoting absorption of glucose
in the intestinal tract; increases glucose
absorption from the intestines
- Secreted and synthesized by the thyroid
follicles of the thyroid gland; stimulates
glycogenolysis and gluconeogenesis
Blood Glucose Determination
The normal values for glucose as determined
by the most sensitive method today are as follows:
Serum or plasma: 50 110 mg/dL (2.8 6.2 mmol/L)
Conversion factor from mg% to mM = 0.055
Whole blood: lower than serum or plasma by 10%
due to volume occupied by RBCs during
measurement
CSF: 40 70 mg/dL (60 75% of the level in serum or
plasma)
Prompt separation of clot from serum is a
must since glucose is utilized by the RBCs lowering
the value by 5% per hour of serum clot contact.
Delay in glucose testing would require
fluoride or iodoacetate. 2 mg of NaF per ml of whole
blood to prevent glycolysis for 48 hours at 4 deg
Celsius.
Hyperglycemia
• Is an increase in plasma glucose levels
• In healthy patients, during a hyperglycemia state,
insulin is secreted by the ᵝ cells of the pancreatic islet
of Langerhans.
• Insulin enhances membrane permeability to cells
in the liver, muscle and adipose tissue. It also alters
the glucose metabolism pathway.
• Hyperglycemia or increased plasma glucose
levels, is caused an imbalance of hormones
MONTEMAR, T.M.
Categories of diabetes:
• Type 1 diabetes
• Type 2 diabetes
• Other specific types of diabetes
• Gestational Diabetes Mellitus (GDM)
Hypoglycemia
• Hypoglycemia is characterized by low plasma
glucose, usually an overnight plasma glucose of less
than 45 mg/dL (2.5 mmol/L) and an associated
group of symptoms that are relieved by ingestion of
food or carbohydrates. It can occur when insulin
levels are high and glucose production is
inadequate.
• Classic symptoms (Adrenergic & Neuroglycopenic
Symptoms): confusion, seizures, tremors, anxiety,
diplopia, nightmares, dizziness, diaphoresis,
hunger, fatigue, tingling, mental disturbances,
unconsciousness, palpitations, weakness, blurred
vision, headaches
• Hypoglycemia especially the one caused by
insulinoma is diagnosed by the so called Whipple’s
triad.
• Hypoglycemic attacks precipitated by fasting:
Plasma glucose levels of <45 mg/dL (2.5 mmol/L)
• Symptoms relieved promptly by glucose
administration
• Hypoglycemia involves decreased plasma glucose
levels can have many causes, some are transient
and relatively insignificant, but others can life
threatening.
• The plasma glucose concentration at which
glucagon and other glycemic factors are released is
between 65 and 70 mg/dL at about 50 to 55mg/dL,
observable symptoms of hypoglycemia appear.
• GLUCAGON is released from the islet cells of the
pancreas and inhibits insulin.
• EPINEPHRINE is released from the adrenal gland
and increases glucose metabolism and inhibits
insulin
• S/S: Increase hunger, Sweating, Nausea and
vomiting, Dizziness, Nervousness and shaking,
Blurring of speech and sight, Mental confusion
GLYCOGEN STORAGE DISEASES
TYPE
ENZYME
CLINICAL
DEFICIENT
FEATURES
I (von
Liver & kidney
Hepatomegaly,
Gierke)
Glucose-6lactic acidosis,
phosphatase
hyperlipidemia,
severe fasting
hypoglycemia
II (Pompe)
All tissues’ alpha
Cardiomegaly,
1,4-glucosidase
muscle weakness,
death in infancy
and adults
III (CoriAll tissues’
Hepatomegaly,
Forbes)
debrancher enzyme muscle weakness,
fasting
hypoglycemia
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CC1: CARBOHYDRATES
IV
(Andersen)
V (McArdle)
All tissues’ brancher
enzyme
Muscle
phosphorylase
VI (Hers)
Liver phosphorylase
VII (Tarui)
Muscle and liver
phosphofructokinase
Brain & liver
adenylate kinase
VIII
IX
Liver phosphorylase
kinase
X
Liver and muscle
cAMP-dependent
kinase
Portal cirrhosis,
death in infancy
Pain & stiffness
after exertion;
myoglobinuria
Hepatomegaly,
mild fasting
hypoglycemia
Pain and stiffness
on exertion
Spasticity,
decerebration,
high urinary
catecholamines,
death in infancy
Hepatomegaly,
occasional fasting
hypoglycemia
Hepatomegaly
only
CAUSES OF ABNORMAL GLUCOSE
LEVELS
PERSISTENT HYPERGLYCEMIA
• Diabetes mellitus
• Adrenal cortical hyperactivity (Cushing’s
syndrome)
• Hyperthyroidism
• Acromegaly
• Obesity
TRANSIENT HYPERGLYCEMIA
• Pheochromocytoma
• Severe liver disease
• Acute stress reaction (physical or emotional)
• Shock
• Convulsions
PERSISTENT HYPOGLYCEMIA
• Insulinoma
• Adrenal cortical insufficiency (Addison’s disease)
• Hypopituitarism
• Galactosemia
• Ectopic insulin production from tumors
TRANSIENT HYPOGLYCEMIA
• Acute alcohol ingestion
• Drugs: salicylates, antituberculosis agents
• Severe liver disease
• Several glycogen storage disease
• “Functional” hypoglycemia
• Hereditary fructose intolerance
Gestational diabetes mellitus (GDM)
• GDM is the onset of diabetes mellitus during
pregnancy.
• After childbirth, the individual generally returns to
normal metabolism. However, there is an increased
chance that type 2 diabetes mellitus may develop
later in life.
A. Glycogen storage diseases, of which there are 10
types, are inherited diseases involving the deficiency
of particular enzymes; these deficiencies cause
defects in the normal metabolism of glycogen.
• von Gierke, type I: Glucose-6-phosphatase
deficiency
• Pompe,
type
II:
a-1,4-glucosidase
deficiency
• Cori, type III: Amylo-1,6-glucosidase
deficiency
B. Galactosemia
• a cause of failure to thrive syndrome in
infants, is a congenital deficiency of one of
three enzymes involved in galactose
metabolism, resulting in increased levels of
galactose in plasma.
• The most common enzyme deficiency is
galactose-1-phosphate uridyl transferase.
• Galactosemia occurs because of the
inhibition of glycogenolysis and is
accompanied by diarrhea and vomiting
Microalbuminuria
• Microalbumin measurements are useful to assist in
diagnosis at an early stage and before the
development of proteinuria.
• Microalbuminuria is defined as persistent
albuminuria in the range of 30 to 299 mg/24 hr or an
albumin creatinine ratio of 30 to 300 μg/mg.
• Clinical proteinuria or macroalbuminuria is
established with an albumin-creatinine ratio of ≥300
mg/24 h or an albumin-creatinine ratio of ≥300
μg/mg.
KETONES
• Ketone bodies are produced by the liver through
metabolism of fatty acids to provide a ready energy
source from stored lipids at times of low
carbohydrate availability.
• Types: Acetone (2%), Acetoacetic acid (20%), 2-ßhydroxybutyric acid (78%)
• A low level of ketone bodies are present in the body
at all times. However, in cases of carbohydrate
deprivation or decreased carbohydrate use such as:
Diabetes mellitus, Starvation/fasting, High-fat diets,
Prolonged vomiting, Glycogen storage disease
• Ketonemia refers to accumulation of ketones in
blood.
• Ketonuria refers to accumulation of ketones in
urine.
Renal Threshold for Glucose
1. Glucose is filtered by the glomeruli, reabsorbed by
the tubules, and normally not present in urine. If the
blood glucose level is elevated, glucose appears in
the urine, a condition known as glucosuria.
2. An individual's renal threshold for glucose varies
between 160 and 180 mg/dL. When blood glucose
reaches this level or exceeds it, the renal tubular
transport mechanism becomes saturated, which
causes glucose to be excreted into the urine.
Inherited disorders of carbohydrate metabolism
MONTEMAR, T.M.
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CC1: CARBOHYDRATES
Methodologies for Glucose Assay
Chemical Methods
a. Copper Reduction
• Folin Wu method - whole blood is
deproteinized using 10% sodium tungstate
and 2/3N sulfuric acid; cuprous oxide formed
is allowed to react in a hot alkaline solution
with phosphomolybdate reagent to produce
phosphomolybdenum blue complex
• Nelson Somoygi/ Somoygi-Nelson serum is deproteinized using 5% zinc sulfate
and 0.3N barium hydroxide; the cuprous
oxide formed is allowed to react with
arsenomolybdate
to
produce
arsenomolybdenum
blue;
the
deproteinization process is able to remove
NGRS measuring true glucose value
• Neocupreine method - adapted to
automation; sample is deproteinized by
tungstate or dialysis; cuprous oxide formed is
allowed to react with neocuproine (2,9
dimethyl 1, 10 phenanthroline hydrochloride)
to form a yellow to orange product
• Benedict – modification of Folin-Wu
employed in testing urine sugars
• Schaeffer-Hartmann-Somoygi
–
titrimetric method using iodine to oxidize
cuprous oxide formed and the excess iodine
in the blank and the sample is titrated with
thiosulfate
b. Ferric Reduction (Hagedorn Jensen)
- uses ferricyanide ions instead of
cupric ions; the yellow ferricyanide is
reduced to colorless ferrocyanide solution
and the decrease in absorbance is monitored
- ferrocyanide offers advantage over
cuprous ions by being less reoxidizable by air
c. Condensation method
• Dubowski (Ortho-toluidine method)
– glucose condenses with an aromatic
amine, o-toluidine in hot glacial Hac to
produce a green colored N-glycosylamine
and a Schiff’s base; considered as the most
specific nonenzymatic for glucose
• Anthrone condensation – glucose is
converted into hydroxymethlyfurfural in hot
strong acid and reacts with the enol tautomer
of anthrone to form a green product
Enzymatic Methods
a. Glucose oxidase (GOD) Coupled Reaction
- GOD converts glucose, in the presence of
oxygen, into gluconic acid and hydrogen
peroxide. In the presence of the enzyme
peroxidase, a reduced chromogen is
oxidized to give a colored compound; vitamin
C interferes in the test
- Chromogens that can be used are:
MONTEMAR, T.M.
*p-aminophenazone (PAP) which is oxidized
to a quinone imine dye (pink to red)
*o-dianisidine which is oxidized to an orange
product;
*o-toluidine which is oxidized to a green
product;
*indophenol blue which is oxidized to a blue
product
*iodide which is oxidized into a purple
product
• Polarographic GOD Method
- This is based on the consumption of
oxygen during the enzyme catalysis of
glucose conversion
- The oxygen consumed is monitored using a
Clark electrode (amperometric technique)
GOD
Glucose + O₂ → Gluconic acid + H₂O₂
To prevent the regeneration of oxygen to hydrogen
peroxide, either of the following is done.
catalase
H₂O₂ + ethanol
→
Acetaldehyde + H₂O
molybdate
H₂O₂ + 2H+ + 2I
→
I₂+ H₂O
• Colorimetric (Trinder Reaction)
b. Hexokinase-G6PD
- The most specific method and therefore the
reference method for glucose determination
- Glucose is phosphorylated in the presence
of hexokinase and magnesium ions to form glucose
6-phosphate; the G-6-P formed is acted upon by G6-PD to form 6-phosphogluconolactone with the
reduction of NAD or NADP.
hexokinase
glucose + ATP →
glucose-6-phophate + ADP
G6PD
Glucose-6-phosphate
+
NAD
→
6phosphogluconolactone
+ NADH
(NAD can be NADP) (and NADH can be NADPH)
− Glucose in the solutions exists either as an
alpha-glucose or beta glucose.
− Alpha glucose is approximately 35% of
total glucose; beta glucose is 65%.
− Glucose oxidase is specific to glucose.
• Alpha glucose is converted into beta
glucose using the enzyme MUTAROTASE
o Presence of OXIDIZING and
REDUCING AGENTS interfere with glucose oxidase
method.
o
HEMOLYZED and ICTERIC
SPECIMENS cause decreased glucose with
Hexokinase- G6PD method
Laboratory Tests used to Assess Glucose
Metabolism
1. RANDOM BLOOD GLUCOSE ~ blood glucose
taken any time of the day and without any fasting;
often used for emergency cases
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CC1: CARBOHYDRATES
2. FASTING BLOOD GLUCOSE ~ taken after at
least 8 hours fasting; usually done in the morning, to
prevent the effects of diurnal variation caused by
hormones
3. ORAL GLUCOSE TOLERANCE TEST ~ a series
of glucose testing; a fasting blood glucose is
determined after 8- 10 hours of fast; glucose load is
given; series of blood samples for glucose assays
are then collected 30 minutes, 1 hour and 2 hours
after glucose load intake
4. 2 HR POSTPRANDIAL GLUCOSE -fasting blood
sugar is initially; patient is then given glucose load
(usually 75g) and plasma glucose is determined
after 2 hours. normally, blood glucose levels should
be back to reference limits 2 hours post load
5.
Glycosylated
hemoglobin
(glycated
hemoglobin)- used for long term monitoring of
glucose control over the previous 3-4 months. it is
formed by attachment of glucose at the end or both
N-terminal valines of the beta chains of normal adult
hgb. for every 1% increase in HbA1c, there is a
35mg/dl change in plasma glucose. patients with
Hemolytic anemia have falsely decreased HbA1c.
specimen is EDTA-WHOLE BLOOD; can be
measured by electrophoresis, isoelectric focusing,
HPLC, spectrophotometry and RIA
6. FRUCTOSAMINE (glycated albumin)- used for
short term monitoring glucose control over the
previous 2-3 WEEKS since albumin has a life span
of 20 days in the circulation; affected by changes in
albumin levels; patients with HYPOALBUMINEMIA
has decreased glycated albumin results; represents
glucose complexed with other proteins
7. RBS – no fasting requirement; normal range is 45
– 130 mg/dL (2.5 – 7.2 mmol/L)
Guidelines for Oral Glucose Tolerance Test
• Patient is asked to consume a normal to high
carbohydrate intake 150G carbohydrates per day for
3 days prior to the test)
• Patient should discontinue, if possible, medications
known to affect glucose tolerance
• Patient is asked to fast overnight and to avoid
excessive physical activity. Patient should fast at
least 8- 10 hours but not greater than 16 hours.
• OGT testing should be performed on the morning
to prevent hormonal diurnal effect on glucose. Blood
glucose is taken every 30 minutes for 2 hours.
• Patient should be ambulatory. Patient should
refrain from exercise, eating or drinking (except
water) and smoking
• Fasting blood glucose is measured before giving
the glucose load; a fasting glucose of greater than
140, test should be terminated; fasting glucose of
less than 140mg/dL. Glucose load should be given
to the patient
MONTEMAR, T.M.
• Glucose load for an adult is 75G. Children receive
1.75g per kg of body weight, max of 75g.
• Patient should finish drinking the glucose load
within 5-15 MINUTES
• Patient should not vomit. If patient vomits,
discontinue the test.
Categories of Oral Glucose Tolerance
Normal
glucose 2-h PG <140 mg/dL (<7.8
tolerance
mmol/L)
Impaired glucose 2-h PG 140-199 mg/dL (7.8tolerance
11.1 mmol/L)
Provisional
2-h PG ≤200 mg/dL ( ≤11.1
diabetes diagnosis mmol/L)
Diabetes Mellitus
Diabetes mellitus is a group of diseases in which
blood glucose levels are elevated due to efficiency
in insulin action.
Classical manifestations (3 Ps)
- Polyuria
- Polydipsia
- Polyphagia
Comparison between Type 1 and Type 2 DM
TYPE 1 DM
TYPE 2 DM
Synonym
IDDM, JOD
NIDDM, adultonset diabetes
Age of onset During puberty
Usually after
or childhood
age 35
(gradual)
Physique
Frequently
Obese
during onset
emaciated
Prevalence
10-20% of
80-90% of
diagnosed
diagnosed
diabetics
diabetics
Genetic
Moderate
Very strong
predisposition
HLA
present
Usually absent
association
Defect
Ketosis
Plasma
insulin level
Acute
complications
Oral
hypoglycemic
drugs
Treatment
with insulin
Vasculature
affected
TYPE 1 DM
Beta cells are
destroyed
Common
Low to absent
TYPE 2 DM
Beta cells unable
to produce insulin
Rare
Normal to high
Ketoacidosis
Unresponsive
Hyperosmolar
coma
Responsive
Always
necessary
Microcirculation
Usually not
required
Macrocirculation
Complications of DM are:
1. end stage renal disease
2. nontraumatic amputation
3. new blindness in adults aging 20 74 years old
4. diabetic neuropathy in 60 70% of patients
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CC1: CARBOHYDRATES
5. atherosclerotic disease and
6. 2 to 4 times predisposition to heart and
cardiovascular diseases.
-
Criteria to Diagnose DM
FBS greater than or equal to 126 mg/dL (7.0
mmol/L) on at least two occasions
2 Hr PP (2 Hour Postprandial test) glucose greater
than 140 mg/dL (7.8 mmol/L)
Symptoms of hyperglycemia (3 Ps), unexplained
weight loss plus a casual or RBS greater than or
equal to 200 mg/dL (11.1 mmol/L)
A two-hour post load glucose of 200 mg/dL or
greater in OGTT
Exceptions to these criteria is the diagnosis of
gestational diabetes mellitus (GDM) which is present
in 4% of all pregnancies
-
Criteria for the diagnosis of diabetes mellitus
1. Symptoms of diabetes plus a random plasma
glucose level of ≥200 mg/dL (<11.1 mmol/L)
2. A fasting plasma glucose of ≥126 mg/dL (<7.0
mmol/L)
3. An oral glucose tolerance test with a 2-hour post
load level ≥200 mg/dL. (<11.1mmol/L)
Tests used to Diagnose DM
FBS = 50 110 mg/dl (2.8 6.2 mM) requires an 8 hour
fasting
2-Hr Postprandial test = glucose measurement is
performed two hours after a meal; highest glucose
level is reached 60-90 minutes after a meal and
similar to FBS after 2 hours
Oral
glucose
tolerance
test
(NDDG
Recommendation):
1. Patient to be tested should be on a regular
diet ingesting at least 150 g or carbohydrate
3 days prior to testing.
2. Patient must fast the night before the testing
is performed.
3. The patient is challenged orally with 75 g
glucose (glucola) during the test to be taken
in 5 minutes.
4. Patient should not eat food, drink tea, coffee
or alcohol.
5. Vigorous exercise and cigarette smoking are
not allowed.
6. Venous blood samples collected during the
process are preferably collected in gray top
tubes
A baseline glucose level is obtained prior
testing and further blood samples are taken after 30
minutes, 1 hour, 11/2 hours and 2 hours.
The patient should rest throughout the test
Diagnosis of DM in a patient if these are met:
FBS is > 126 mg/dl, and
2 Hr PP value is ≥200 mg/dl, or
a level between 0 2 hours is ≥200 mg/dl
IVGTT
- Indicated in cases who have malabsorptive
syndromes or previous gastric or intestinal
surgery
MONTEMAR, T.M.
-
-
20% glucose solution is IV introduced in 3
minutes
Blood is withdrawn in 0,3,5,10,20,30,40,60
and 120 minutes
Glucose disappearance constants (k values)
are calculated from the plot of the logarithm
of glucose concentration against time
K value of <1.2 indicates DM
Different Criteria for Diagnosing DM by the OGTT
National Diabetes Data Group
Fajans and Conns
Wilkerson point system
Siperstein
O’ Sullivan (pregnancy)
New Categories of Impaired Fasting Glucose
(IFG) and Impaired Glucose Tolerance (IGT) as
recommended
by
American
Diabetes
Association (ADA)
FBS, 110 125 mg/dl …………. IFG
2-Hr PP, 140 199 mg/dl ……... IGT
Criteria for the Testing and Diagnosis of
Gestational Diabetes Mellitus
• The diagnostic criteria for gestational diabetes
follow the guidelines established by the American
College of Obstetrics and Gynecology.
• Only high-risk patients should be screened for
GDM.
o Age older than 25 years
o Overweight
o Strong family history of diabetes
o History of abnormal glucose metabolism
o History of a poor obstetric outcome
o Presence of glycosuria
Diagnosing GDM
Screening test for Gestational DM
Do the 1 hour OGTT with 50 g. glucose load; prior
fasting not required
<140 mg/dl ….. GDM ruled out
>140 mg/dl ….. GDM possible; do diagnostic
test
Diagnostic test for Gestational DM
Do the 3 hr OGTT with 100 g. glucose load;
overnight fasting is required
GDM is confirmed if plasma glucose is at or above
cutoff value (140 mg/dl) for two or more samples
Specimen Considerations and Patient
Preparation
• Samples: whole blood, serum, plasma, urine, CSF
and synovial fluid
• Standard clinical specimen is fasting venous
plasma.
• FBS should be obtained after 8-10 hrs of fasting.
• Whole blood gives approximately 10%-15%
LOWER glucose levels than serum or plasma.
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CC1: CARBOHYDRATES
• Serum is appropriate for glucose analysis if it is
separated from the cells within 30 to 60 minutes
• 2 mg of sodium fluoride per mL of whole blood
prevents glycolysis for up to 48 hrs.
• Fluoride binds magnesium, which causes inhibition
of the enzyme enolase.
• Glucose is metabolized at room temperature at a
rate of 7mg/dl/hr
• At 4°C, glucose decreases by approximately
2mg/dl/hr.
• CSF glucose concentration is approximately 60%70% that of plasma concentrations.
• Blood for glucose analysis should be collected
approximately 1-2 HRS BEFORE the spinal tap
CATEGORIES OF FASTING PLASMA GLUCOSE
• Normal Fasting Glucose = Fasting Plasma
Glucose <110 mg/dL
• Impaired Fasting Glucose = Fasting Plasma
Glucose ≥110 mg/dL and < 126 mg/dL
• Provisional Diabetes Diagnosis = Fasting Plasma
Glucose ≥126 mg/dL
METHODS of KETONE MEASUREMENT
• The specimen requirements is fresh serum or
urine: the sample should be tightly stoppered and
analyzed immediately. No method used for
determination of ketones reacts with all three ketone
bodies.
• historical test (Gerhardt’s) used ferric chloride
reacted with acetoacetic acid to produce a red color.
Methods for microalbuminuria
• random spot collection for the measurement of the
albumin –creatinine ration is preferred method
• 24-hour collection
• time 4-hour overnight collection
o
A patient is determined to have
microalbuminuria when two of three
specimens collected within 3- to 6- month
period are abnormal.
o Factors that may elevate the urinary
excretion of albumin include: exercise within
24 hours, infection, fever, congestive heart
failure, marked hyperglycemia, and Marked
hypertension.
Others Methods
• Islet autoantibody testing is not currently
recommended for routine screening for diabetes
diagnosis.
oThe presence of autoantibodies to the ᵝ
islet cells of the pancreas is characteristics of
type 1 diabetes.
• Insulin measurements are not required for the
diagnosis of diabetes mellitus, but in certain
hypoglycemic states, it is important to know the
concentration of insulin in relation to the plasma
glucose concentration.
MONTEMAR, T.M.
7