Clinical diagnostic biochemistry - 2
CLS 334
Dr. Maha Al-Sedik
2015
Oral Glucose Tolerance Test
Serial measurement of plasma and urine glucose before and after a
specific amount of glucose given orally.
Indications :
1- Diagnosis of impaired glucose tolerance.
2- Diagnosis of gestational D.M.
3- Diagnosis of unexplained glucosuria.
4- Unexplained nephropathy, retinopathy or neuropathy.
Precautions before test :
1- Unrestricted diet 3 days before.
2- No drugs affecting glucose level.
3- No smoking or excessive exercise in the day of the test.
How to do the test :
1- Fasting 8 – 12 hours. Measure blood and urine glucose.
2- Give glucose load (50 – 100 g glucose or 1 g/kg body weight)
dissolved in 250 – 300 ml water.
3- Blood and urine samples are taken every 1 hr for 2or 3 hours.
Blood glucose level is plotted against time to draw glucose
tolerance curve.
Normal curve :
• Fasting: 70 – 100 mg / dl
• Peak: 130 – 155 mg / dl after 1 hour
• Less than 140 mg l dl after 2 hours
• All urine samples contain no glucose.
Abnormalities in OGTT
1.Diabetic curve:
Fasting: more than 126.
After 2 hours: more than 200.
One or more urine samples contain glucose.
2. lag storage response:
It characterized by a sharp raise in blood glucose in the
first hour with peak value exceeding the renal threshold
with appearance of glucose in urine and return to normal
fasting or below fasting occur in the second hour. This is
due to rapid absorption of glucose from intestine.
It occurs in:
Post-gastrectomy.
 Hyperthyrodisim & stress.
3- Flat response
There is an ↑ in glucose tolerance or failure of the
plasma glucose level to raise significantly after an
oral glucose load and return the fasting level is rapid
this is due to:
 Insulinoma.
 intestinal malabsortion syndrome.
Diabetes Mellitus
Diabetes mellitus is a group of metabolic disorders of carbohydrate
metabolism in which glucose is underused, producing hyperglycemia.
Some patients may experience acute life threatening hyperglycemic
episodes, such as ketoacidosis.
Classification:
Type 1 diabetes.
Type 2 diabetes.
Gestational diabetes mellitus (GDM).
Impaired glucose tolerance (IGT).
Criteria for the Diagnosis of Diabetes Mellitus
 Diabetes Mellitus
• Classic symptoms of diabetes.
• Fasting plasma glucose > 126 mg/dL (7mmol/L).
• 2-hour post prandial plasma glucose concentration > 200 mg/dL
(11.1 mmol/L).
1- Type I D.M.
 Old names: Insulin dependent (IDDM).
 Usually starts acutely in young people <30 years but may start at
any age.
 There defective insulin secretion or destruction of B-cells.
 Most individuals have antibodies that identify autoimmune
process.
Pathogenesis of Type 1 Diabetes Mellitus
Antibodies
• Islet cell cytoplasmic antibodies (ICAs)
• Insulin autoantibodies (IAAs)
Genetics
HLA-DR3 or HLA-DR4 histocompatibility antigens.
Environment
2- Type II D.M. :
 Old names : Non-insulin dependent D.M. (NIDDM) , adult onset
or maturity onset D.M.
 Insulin secretion is slightly affected but there is impaired insulin
action due to insulin resistance.
 Usually starts over 40 years.
Pathogenesis of Type 2 Diabetes Mellitus
 Decrease of β-Cell Function.
 Insulin Resistance
Insulin resistance is defined as a decreased biological response to
normal concentrations of circulating insulin, is found in both
obese, non-diabetic individuals and patients with type 2 diabetes.
 Environment: Diet and exercise.
 Diabetogenes:
Insulin-Resistance Genes.
Body gain genes.
Gestational Diabetes Mellitus
Screening
 Perform between 24 and 28 week of gestation on all averageand high-risk pregnant women not identified as having glucose
intolerance.
 Give 50 g oral glucose load without regard to time of day or time
of last meal.
 Measure venous plasma glucose at 1 hr.
 If glucose is >140mg/dL, perform glucose tolerance test for
pregnant womem.
Diagnosis
 Perform in the morning after a 8 hr fast.
 Measure fasting venous plasma glucose.
 Give 75 or l00g of glucose orally.
 Measure plasma glucose hourly for 3hr if you give 100 g (or 2hr
if 75 g of glucose given).
 At least two values must meet or exceed the following:
100-g load
75-g load
Fasting
95mg/dL
95mg/dL
1 hr
180mg/dL
180mg/dL
2 hr
155mg/dL
155mg/dL
3 hr
140mg/dL
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Pre diabetes
Prediabetes is when blood glucose levels are higher than normal
but not high enough for a diagnosis of diabetes. Prediabetes
means a person is at increased risk for developing type 2
diabetes, as well as for heart disease and stroke. Many people
with prediabetes develop type 2 diabetes within 10 years.
Normal
Fasting
Post - prandial
Pre - diabetes
Diabetes
Less than 100
mg/dl
100 – 126 mg / dl
More than 126 mg / dl
Less than 140 mg
/dl
140 – 199 mg / dl
More than 200 mg / dl
Keton bodies
acetoacetic acid
 -hydroxy butyric acid
acetone
Ketogenesis
 It is the formation of ketone bodies.
 Site of ketogenesis: liver mitochondria.
 The ketone bodies are acetoacetate, b-hydroxybutyrate, and
acetone.
Importance of keton bodies:
1. When carbohydrates are low , the keton bodies are used as fuel.
2. Acetoacetate and beta-hydroxy buterate are important in
biosynthesis of neonatal cerebral lipids.
3. In early stage of starvation , the heart and skeletal muscles use
keton bodies as source of energy to keep glucose enough for
brain as long as possible.
Steps of synthesis of Ketone bodies:
1. Two molecules of acetyl CoA react with each other in the
presence of thiolase enzyme to form acetoacetyl CoA.
2.Condensation of acetoacetyl CoA with acetyl CoA to
form HMG CoA (3 hydroxyl- 3 methyl glutaryl CoA)
catalyzed by HMG CoA synthetase,
3. HMG-CoA lyase enzyme catalyzes the cleavage of
HMG-CoA to acetoacetate and acetyl CoA.
4. Acetoacetate produces β-hydroxybutyrate in a reaction
catalyzed by β-hydroxybutyrate dehydrogenase in the
present NADH.
5. Both acetoacetate and β-hydroxybutyrate can be
transported across the mitochondrial membrane
and the plasma membrane of the liver cells,
enter to the blood stream to be used as a fuel by other
cells of the body.
6. In the blood stream, small amounts of
acetoacetate are spontaneously (non- enzymatically)
decarboxyated to acetone.
 Acetone is volatile and can not be detected in the
blood.
 The odor of acetone may be detected in the breath
and also in the urine of a person who has high level
of ketone bodies in the blood.
 e.g. in severe diabetic ketoacidosis, while under
normal conditions, acetone formation is negligible.
Ketolysis
Ketolysis is the complete oxidation of ketone bodies to C02
and water.
Site:
Mitochondria of extrahepatic tissues but not in the liver
due to deficiency of the enzymes needed for ketolysis.
KETOSIS (KETOACIDOSIS)
ketonemia: Excessive formation of ketone bodies results
in increased blood concentrations.
ketonuria: increased excretion of ketone bodies in the
urine.
Diabetic ketoacidosis
Hyperglycemia
Ketosis
Acidosis ↑ K
Signs and symptoms:
1-Classic symptoms of hyperglycemia:
polyuria , polydipsia , polyphagia and dry skin.
2-Symptoms of hyperkalemia:
arrhythmia
3- Symptoms of acidosis:
Acidotic breath ( deep and rapid) , confusion , arrhythmia and may
lead to coma.
4- Symptoms due to increase in keton bodies:
-Nausea, vomiting and abdominal pain.
- fruit smell of mouth.
- Disturbed consciousness and confusion.
5- Symptoms of dehydration:
-Skin: Dry, hot and flushed skin.
-Tongue: Dry (sometimes woody tongue).
-Eyes: Sunken eyes and dark circles under the eyes.
LAB VALUES IN DKA:
• Blood glucose is > 300 mg/dl•
• Serum ketones are positive.
• Arterial pH is < 7.3
• Potassium is high.
Reference:
Burtis and Ashwood Saunders, Teitz fundamentals of Clinical
Chemistry, 4th edition, 2000.