ORAL GLUCOSE TOLERANCE TEST AND APPLICATIONS

Question 1

What is OGTT?

Answer 1

It is a test done to assess the ability of the body to handle extra oral glucose load

It is a stress and challenge test

Question 2

INDICATIONS FOR OGTT

Answer 2

Patient may have symptoms suggestive of DM
Repeated Fasting plasma glucose values are inconclusive of DM 6.1 - 6.9mmol/L
Excessive weight gain in pregnancy with past history of macrosomia or fetal loss
To rule out benign renal glycosuria

Question 3

Normal Response curve

Answer 3

1. Initial fasting glucose within normal limits.
2. The highest peak value is reached within 1 hour
3. The highest value does not exceed the renal threshold (160-180mg/dl)
4. The fasting level is against reached by 2-2.5 hours.
5. No glucose or ketone bodies are detected in any specimen of urine.

Question 3

Resonse of diabetic patients

Answer 3

1. Fasting blood glucose is definitely raised above 110 mg/dI.
2. Highest peak reached at 1 1/2hr
3. The highest value exceed the renal threshold.
4. The blood glucose level dose not return to fasting level within 2.5 hours.
   This is the most characteristic feature of DM.
5. Urine sample always contains glucose except in some chronic diabetes or nephritis who may have raised renal threshold.
   According to severity, GTC may be :
   Mildely diabetic curve
   Moderately severe diabetic curve
   Severe diabetic curve

Question 3

Procedure for OGTT?

Answer 3

GENERAL INSTRUCTIONS
* When the patient was given a OGTT appointment they should have been adequately briefed about the test.

1. The patient should be on a high carbohydrate (>150g/day) diet for three days prior to testing.
2. The patient must be allowed to lead his normal life before the day of the test
3. The patient must fast overnight for at least 10 hours (but not more than 16 hours) and remain so during the entire test period.
4. If patient is on drugs known to affect glucose metabolism, it should be discontinued for the period of the test. This is done after consultation with the prescribing Physician
   Inform the patient that they must sit quietly and not eat, drink (except water) or smoke for the duration of the procedure.

Question 4

Procedure ON THE DAY OF THE TEST

Answer 4

1. Ensure that the patient has fasted overnight and explain test protocol to them.
2. Take a venous fasting sample for estimation of basal glucose level. Label appropriately.
3. The equivalent of 75g anhydrous glucose is dissolved in 250mL of drinkable water. The patient must drink this in about 5 minutes.
4. Subsequently blood samples are obtained half hourly for two hours and properly labelled.
5. Urine sample is also obtained at one hour into the test
6. The plasma glucose concentrations of the samples are determined.
7. OGTT curve is then plotted of the plasma glucose against time.

Question 4

Lag curve

Answer 4

1. Fasting glucose level is normal.
2. Raises rapidly in the ½ to1 hour an exceed the renal threshold so that the corresponding urine specimens show glucose.
3. Above renal threshold
4. The return to normal value is rapid and complete.
   • The curve is obtained in :
   • Hyperthyroidism
   • After gastroenterosectomy
   • During pregnency
   • Also in early diabetes
5. Glucosuria present

Question 5

OTHER TYPES OF GTT

Answer 5

• Intravenous Glucose Tolerance Test
• Gestational 2 hour receive a 75g (10 oz) dose with a Blood Glucose level at the following intervals: [0min.] [60min.] [120min.]
• Gestational 3 hour receive a 100g (10 oz) dose with a Blood Glucose level at the following intervals: [0min.] [60min.] [120min.] [180min.]
• Children (< 12 years) receive a 1.75 g/kg (max 75g or 7.5 oz) dose with a Blood Glucose level at the following intervals: [0min.] [60min.] [120min.]

Question 6

CONTRA-INDICATIONS

Answer 6

• Unaccustomed exercise
• Food
• Drugs that affect carbohydrate metabolism eg Corticosteroids, Diuretics
• Alcohol
• Already diagnosed DM
• In bedridden or severely ill patient
• Patients suffering from an intercurrent infection or the effects of trauma.

Question 6

APPLICATIONS

Answer 6

• To establish the presence of glucose intolerance.
• It is used in patients with borderline fasting and postprandial glucose to support or rule out the diagnosis of diabetes mellitus.
• In unexplained hypertriglyceridemia, neuropathy, impotence, diabetes-like renal diseases, and retinopathy.
• To work up glycosuria without hyperglycemia (eg renal glycosuria).
• It is used to predict perinatal morbidity in pregnancy and to diagnose gestational diabetes.The risks of fetal abnormality and perinatal mortality increase with abnormal carbohydrate metabolism in pregnancy