GLUCOSE TOLERANCE TEST

Department of Pathology
Dr. Meghana. Gowda
• Glucose tolerance means ability to the body to utilize glucose in blood circulation.

• The measurement of plasma glucose before and after a specific amount of glucose given orally should

provide a standard method to evaluate individuals specific values for normal and disease.
• Used in the evaluation of patients with hypoglycemia.

• Patients with a family history of diabetes.

• Patients who are massively obese.

• Patients with a history of recurrent infections.

• Patients with delayed healing of wounds (especially on the lower legs or feet).
• Women who have a history of stillbirths, premature births, or large babies.

• Patients who have transient glycosuria or assist in the diagnosis of diabetes mellitus (DM).

• Hyperglycemia during pregnancy

• Or following myocardial infarction (MI), surgery, or stress.

Contraindications:

a) In proven cases of diabetes mellitus the test is not required.

b) GTT is required only in doubtful cases, it is not recommended for follow up of patient.

c) Patients with serious concurrent infections or endocrine disorders, because glucose intolerance will

be observed even though these patients may not be diabetic.

Potential complications

• Dizziness, tremors, vomiting, sweating, or fainting may occur during testing.

• If these symptoms occur, a blood specimen is obtained, and measure the blood glucose.

• If the glucose level is too high, the test may need to be stopped and insulin administered .
Interfering factors

• Smoking.

• Stress

• Exercise during the test can affect glucose levels.

• Fasting or reduced caloric intake before the GT test can cause glucose intolerance.

• Drugs
Type of glucose tolerance test
• Standard Oral glucose tolerance test

• I/V Glucose tolerance test

• Mini Glucose tolerance test

Patient preparation

• Explain the procedure to the patient.

• Educate the patient about the importance of having adequate food intake with adequate carbohydrates

(150 g) for at least 3 days before the test.

• Instruct the patient to fast for 12 hours before the test.

• Instruct the patient to discontinue drugs (including tobacco) that could interfere with test results.

• Give the patient written instructions explaining the pretest dietary requirements.

• Obtain the patient's weight to determine the appropriate glucose loading dose (especially in children).
Procedure of OGTT

• At about 8 a.m. the fasting blood and urine samples are collected.

• These are called zero samples.

• Administer the prescribed oral glucose solution, usually 75 g of glucose for non-pregnant patients

or 100 g for pregnant patients.

• The glucose dissolve in 300 ml of lemon juice/water mixture within 5min after taking sample .
• In pediatric patients 1.75 g of glucose /kg body weight is given.

• Instruct the patient to ingest the entire glucose load.

• Tell the patient that he or she cannot eat anything until the test is completed.

• However, encourage the patient to drink water.

• No other liquids should be taken during the testing period.

• Inform the patient that tobacco, and smoking are not allowed.

• Collect a venous blood & urine sample at 30 min. interval for up to 150 min.

• Glucose is estimated in all the blood samples.

• Urine is analyzed for the presence of glucose.

LABORATORY PROFILE OF A NORMAL PERSON AFTER GLUCOSE LOAD

• Fasting 30 min. 60 min. 90 min. 120 min. 150 min.

• Blood Glucose (mg/dl) 75 130 150 110 90 70

• Urinary Glucose nil nil nil nil nil nil

NORMAL GLUCOSE TOLERANCE CURVE

• 0 50 100 150 200 250 300 350 400 0 30 60 90 120 150 Glucose conc .in mg/dl Time of
sample in min.

• Fasting blood glucose (zero hour sample) is75mg/dl. Which is well with in the normal range

(normal 60-100mg/dl).

• There is rise of blood glucose after glucose load and the peak value is observed at I hour.
NORMAL GLUCOSE TOLERANCE

• Normally there is a rapid insulin response to the ingestion of a large oral glucose load.

• This response peaks in 30 to 60 minutes and returns to normal in about 3 hours.

• Patients with an appropriate insulin response are able to tolerate the dose quite easily, with only

a minimal and transient rise in plasma glucose levels within 1 to 2 hours after ingestion.

• Glucose will not spill over into the urine in normal patients .
LABORATORY PROFILE OF A DIABETC PATIENT AFTER GLUCOSE LOAD

Moderate Diabetic Curve

• Fasting 30 min. 60 min. 90 min. 120 min. 150 min.

• Blood Glucose (mg/dl) 130 200 280 260 220 170

• Urinary Glucose nil ++ ++ ++ ++ nil

Severe Diabetic Curve

• Fasting 30 min. 60 min. 90 min. 120 min. 150 min.

• Blood Glucose (mg/dl) 230 300 345 365 350 330

• Urinary Glucose ++ +++ +++ +++ +++ +++

LABORATRORY PROFILE OF A PATIENT HAVING RENAL GLYCOSURIA

• Fasting 30 min 60 min 90 min 120 min 150 min 180 min

• Blood Glucose (mg/dl) 90 130 150 140 120 100 90

• Urinary Glucose nil + + + + ± nil

RENAL GLYCOSURIA

• Blood glucose levels are within the normal limits but urine glucose is positive.

• Glucose tolerance curve is normal.

• Thus glucose is found in some of the samples depending upon the renal threshold.

• There is lowering of renal threshold due to renal tubular defect in glucose absorption.

• GTT is also useful in the diagnosis of this inherited renal tubular defect.
CAUSE OF RENAL GLYCOSURIA

• Early diabetes mellitus

• Pregnancy

• Renal disease

• Heavy metal poisoning

• Deficiency of carrier protein (SGLT-2).

• Renal glycosuria can also be observed in children of diabetic parents.

LABORATRORY PROFILE OF A PATIENT HAVING LAG CURVE

• Fasting 30 min 60 min 90 min 120 min 150 min 180 min

• Blood Glucose (mg/dl) 90 230 180 150 120 100 90

• Urinary Glucose nil + + nil nil nil nil

LAG CURVE

• Fasting blood glucose is normal.

• Sharp rise within 30 minutes to one hour

• The blood glucose levels exceed the renal threshold.

• The decline is rapid and the normal levels are attained back.

• Some of the urine samples contain glucose, where the blood glucose is above the renal threshold.

• This is due to an increased rate of glucose absorption from the gut (sometimes in hyperthyroid).

• The increase in blood glucose is due to delay in insulin action.

• Insulin function lagging behind, hence called Lag Curve

CAUSE OF LAG

• Hyperthyroidism

• Pregnancy

• After gastro-enterostomy

• Early diabetes mellitus

FLAT CURVE

• Fasting blood is ≤80 mg/dl.

• All samples show low blood glucose.

• Urine glucose is negative.

• Flat curves are seen in patients with hypoactivity of other endocrine organs.

e.g. in hypopituitarism and Addison’s disease, malabsorption.

IV GLUCOSE TOLERANCE TEST

• This test is undertaken for patients with malabsorption

• Under these conditions oral glucose load is not well absorbed and the results of oral glucose

tolerance test become inconclusive.

• The values for the IV GT test differ slightly from those of the oral GT test because IV glucose is

absorbed faster.
PROCEDURE

• I/V glucose tolerance test is carried out by giving 25 g of glucose dissolved in 100 ml intravenous

injection within 5 minutes.

• Completion of infusion is taken as 0 time.

• Blood samples are taken at 10 minutes interval for the next hour.

• The peak value is reached within a few minutes and the value touches to near normal in 45-60 minutes.
INTERPRETATION

• In normal individuals, blood glucose level returns to normal within 60 minutes.

• In diabetes mellitus, decline is slow.

• The initial values are attained in 120 minutes.

CLINICAL SIGNIFICANCE

Decrease Glucose Tolerance

• Diabetes mellitus (DM): This disease is defined by glucose intolerance and hyperglycemia.
• Acute stress response
• Cushing syndrome
• Chronic renal failure
• Glucagonoma
• Acute pancreatitis
• Diuretic therapy
• Corticosteroid
• Myxedema
• After gastrectomy.
Increased Glucose Tolerance

Increased carbohydrate tolerance is observed in all conditions that cause hypoglycemia:-

• Hypopituitarism

• Hyperinsulinism

• Hypothyroidism

• Adrenal Cortical Hypofunction