Oral Glucose Tolerance Test PDF

Suez Canal University Faculty of Medicine Oral Glucose Tolerance Test At the end of this lab students will know: 1. Definition of OGTT 2. Indications 3. Procedure 4. Normal Su...

Suez Canal University Faculty of Medicine Oral Glucose Tolerance Test At the end of this lab students will know: 1. Definition of OGTT 2. Indications 3. Procedure 4. Normal Sugar Curve 5. Diabetic Curve 6. Renal Glucosuria Department of Biochemistry and Molecular Biology  1. Definition When diabetes is suspected, diagnosis can be confirmed by a random blood glucose greater than 200 mg/dl or fasting blood glucose greater than 126 mg/dl. In mild diabetes when there are normal fasting or random glucose levels, Glucose tolerance test (GTT) is indicated. Glucose tolerance test is the test done to check the capacity of the body for utilizing a given amount of glucose & to determine how quickly it is cleared from the blood. Biochemistry and Molecular Biology Department  Glucose tolerance test In a healthy individual, the insulin response to a large oral glucose dose is almost immediate. It peaks in 30 to 60 minutes and returns to normal levels within 3 hours when sufficient insulin is present to metabolize the glucose ingested at the beginning of the test. Biochemistry and Molecular Biology Department  2. Indications It is used for: 1- Detection of mild diabetes when there are normal fasting or random glucose levels. 2- To ascertain the renal threshold for glucose It is indicated if: 1. Family history of diabetes. 2. Obesity. 3. Unexplained episodes of hypoglycemia. 4. History of recurrent infections (boils & abscesses) 5. In women, history of delivery of large infants, stillbirths, neonatal death, and premature labor. 6. Transitory glycosuria or hyperglycemia during pregnancy, surgery, trauma, stress, and MI. Biochemistry and Molecular Biology Department  Procedure 1. The patient is instructed not to restrict carbohydrate intake in the days or weeks before the test 2. Ensure that the following drugs are discontinued 3 days before the test because they may influence test results e.g. hormones, oral contraceptives, steroids.. etc 3. Insulin and oral hypoglycemic should be withheld until the test is completed and the test should not be done during an illness. Biochemistry and Molecular Biology Department 4. Record the patient's weight. a. Pediatric doses of glucose are based on body weight, calculated as 1.75 g/kg not to exceed a total of 75 g. b. Pregnant women: 100 g glucose c. Nonpregnant adults: 75 g glucose 5. Samples of blood and urine are then taken every 0.5- 1 hour for 2 hours and each is estimated for its glucose content. 6. A curve is prepared showing the relation between blood glucose in mg% and time in hours. Biochemistry and Molecular Biology Department  A-NORMAL BLOOD SUGAR CURVE 1. Fasting blood glucose 70-100 mg% 2. A gradual increase to a peak which is reached after 0.5- 1 hour. 3. This peak amounts to 120-140 mg% i.e. always below the renal threshold (180 mg%). 4. The gradual rise in concentration of blood glucose seen is due to increased rate of absorption of glucose from intestine which exceeds the rate of utilization by tissues. Biochemistry and Molecular Biology Department  A-NORMAL BLOOD SUGAR CURVE 5. A gradual decrease to the fasting level is started after the peak is reached. This is due to release of insulin from the beta-cells of pancreas. This released insulin produces increased rate of glucose utilization 6. All urine samples are free from glucose. 7. The total duration of curve is about two hours. A decrease below the fasting level may occur after two hours due to overaction or oversecretion of insulin. Biochemistry and Molecular Biology Department  B- DIABETIC BLOOD SUGAR CURVE Mild Diabetes Severe Diabetes 1-Fasting Blood 140-160 mg% 180-200 mg% Glucose 2- Peak : After 1 Hour After 1 Hour Time 200-250 mg% 300-400 mg% Value 3- Return to fasting Not reaching fasting level level after 2 hours 4- Glucose in Urine ++ ++++ In diabetes mellitus there is mild to severe deficiency of insulin with a corresponding decrease in the rate of glucose utilization i.e. decrease tolerance to carbohydrates Biochemistry and Molecular Biology Department  C- CURVE OF RENAL GLUCOSURIA 1- Here there is a congenital defect in renal absorption of glucose from glomerular filtrate. 2- This result from congenital lowering of renal threshold e.g. to 100-110 mg% (normal renal threshold = 180 mg%) 3- The pancreas, insulin release, glucose utilization are normal but there is a glucosuria due to congenital lowering of renal threshold. Biochemistry and Molecular Biology Department  Diabetes Mellitus Renal Glucosuria Lack or deficiency of insulin Congenital lowering of renal 1- Cause i.e. the defect is in the threshold i.e. the defect is in pancreas the kidney. 2- Urine Glucose Present Present 3- Blood Glucose Hyperglycemia Normal or even lowered 4- Pancreas Diseased Normal 5- Kidney Normal Diseased 6- Treatment Insulin Intake Glucose Intake 7- Ketosis Can occur if not treated Can occur if not treated Estimation of blood glucose  Causes of hyperglycemia (1) Alimentary hyperglycemia : After a heavy carbohydrate meal increased rate of glucose absorption temporary hyperglycemia (2) Diabetic hyperglycemia : Hyperglycemia exceeds renal threshold for glucose with passage of glucose in urine, due to defect in insulin. (3) Adrenaline hyperglycemia : During stress adrenaline secretion from adrenal medulla hyperglycemia. Pheochromocytoma: adrenaline secreting tumor  Continue.. (4) Cushing’s syndrome: Glucocorticoids (insulin antagonist), due to hyper function of adrenal cortex. (6) Gigantism and acromegaly: Growth hormone (insulin antagonist) due to hyper function of anterior pituitary. (7) Gestational hyperglycemia: Appears during pregnancy & disappears later after labor.  Hypoglycemia ❖The brain is totally dependent on blood glucose for energy production under physiological conditions. ❖Symptoms and signs of CNS dysfunction occur as result of hypoglycemia. ❖Symptoms of hypoglycemia usually do not occur until (45-75 mg/dL). ❖ Impairment of cerebral function begins when glucose is < 50 mg/dL.  Causes of hypoglycemia Side effect of drugs used for the treatment of diabetes Extensive liver disease Hypothyroidism Hypopituitarism Addison’s disease Pancreatic disease or cancer Insulinoma  Serum glucose estimation ❑ Method used: Glucose oxidase method ❑ Specimen: Serum or plasma ❑ Principle: ▪ The enzyme glucose oxidase catalyzes the oxidation of glucose to gluconic acid and H2O2. ▪ Addition of the enzyme peroxidase, phenol and 4 aminoantipyrine result in the formation of colored compound that can be measured at 546 nm. Glucose oxidase Glucose +O2+ H2O Gluconic acid+ H2O2 Peroxidase Quinone +H2O Serum glucose estimation  Serum glucose estimation Mix and incubate for 10 minutes at 37˚C or 30 minutes at room temperature (15-25˚C). Wavelength: 546 nm (490- 550). Measure absorbance of test and standard against reagent blank. glucose concentration (mg/dL) = absorbance of sample× conc. of std absorbance of standard  Specimen precautions ✓ Don’t apply a tourniquet on for a prolonged period of time to avoid decrease in blood glucose level. ✓ Glycolysis in whole blood samples can be prevented by adding sodium fluoride to the specimen to inhibit the glycolytic enzymes. Glycolysis decreases serum glucose by 5-7% in 1 hour at room temperature.  Specimen Precautions ✓ Rapid separation or cooling of the sample will prevent glycolysis. Unhemolyzed samples that have been separated within 30 minutes of drawing are generally considered adequate. ✓ For a fasting blood glucose test, you can’t eat or drink anything but water for eight hours before your test. ✓ Ask about medications that can affect blood glucose levels include: corticosteroids, diuretics. Thank You