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Prakash Mishra

GLUCOSE TOLERANCE TEST

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Glucose tolerance means ability to the body to

utilize glucose in blood circulation.

Glucose tolerance test : The measurement

of plasma glucose before and after a specific

amount of glucose given orally should provide a

standard method to evaluate individuals and

specific values for normal and disease.

GLUCOSE TOLERANCE TEST

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This test is used to assist in the diagnosis of diabetes

mellitus (DM).

It is also used in the evaluation of patients with

hypoglycemia.

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USES

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The GT test may be used for the following condition:

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

hyperglycemia during pregnancy or following myocar

dial infarction (MI), surgery, or stress.

INDICATION OF GLUCOSE TOLERANCE

TEST

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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 end

ocrine disorders, because glucose intolerance will

be observed even though these patients may not

be diabetic.

CONTRAINDICATIONS

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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

.

POTENTIAL COMPLICATIONS

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Smoking.

Stress

Exercise during the test can affect glucose levels.

Fasting or reduced caloric intake before the GT test can

cause glucose intolerance.

Drugs

INTERFERING FACTORS

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Standard Oral glucose tolerance test

I/V Glucose tolerance test

Mini Glucose tolerance test

TYPE OF GLUCOSE TOLERANCE TEST

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Explain the procedure to the patient.

Educate the patient about the importance of having adequat

e 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).

PATIENT PREPARATION

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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 .

PROCEDURE OF OGTT

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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.

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Inform the patient that tobacco, and smoking are not

allowed.

Collect a venous blood &urine sample at 30 min.

interval for upto 150 min.

Glucose is estimated in all the blood samples. Urine is analyzed for the presence of glucose.

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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

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NORMAL GLUCOSE TOLERANCE CURVE

0

50

100

150

200

250

300

350

400

0 30 60 90 120 150

Glu

co

se

co

nc. in

mg

/dl

Time of sample in min.

Glucoseconc.

Fasting blood glucose

(zero hour sample) is 75mg /dl.

Which is well within the normal

range (normal 60-100 mg/dl).

There is rise of blood glucose after

glucose load and the peak value is

observed at Ihour.

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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

.

NORMAL GLUCOSE TOLERANCE

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LABORATORY PROFILE OF A DIABETC

PATIENT AFTER GLUCOSE LOAD

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

BloodGlucose(mg/dl)

130 200 280 260 220 170

Urinary Glucose

nil ++ ++ ++ ++ nil

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

BloodGlucose(mg/dl)

230 300 345 365 350 330

Urinary Glucose

++ +++ +++ +++ +++ +++

Moderate Diabetic Curve

Severe Diabetic Curve

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DIABETIC CURVE

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0

50

100

150

200

250

300

350

400

0 30 60 90 120 150

Glu

cose c

onc.

in m

g/d

l

Time of sample in min.

severe diabetic

Renal thresold

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

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LABORATRORY PROFILE OF A PATIENT

HAVING RENAL GLYCOSURIA

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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.

RENAL GLYCOSURIA

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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.

CAUSE OF RENAL GLYCOSURIA

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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

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LABORATRORY PROFILE OF A PATIENT

HAVING LAG CURVE

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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)

LAG CURVE

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Hyperthyroidism

Pregnancy

After gastro-enterostomy

Early diabetes mellitus

CAUSE OF LAG CURVE

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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.

FLAT CURVE

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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.

IV GLUCOSE TOLERANCE TEST

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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.

PROCEDURE

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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.

INTERPRETATION

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As per current WHO recommendations, in the

mini or modern glucose tolerance test, only two

samples are collected,

Fasting (zero hour) and 2 hour post glucose load.

Urine samples are also collected during the same

time.

The diagnosis is made from the variations

observed in these results.

MINI GTT

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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.

CLINICAL SIGNIFICANCE

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Increased Glucose Tolerance Increased carbohydrate tolerance is observed in

all conditions that cause hypoglycemia:-

Hypopituitarism

Hyperinsulinism

Hypothyroidism

Adrenal Cortical Hypofunction

GLUCOSE TOLERANCE

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Thank you