glucose tolerance test

Professor (Dr.) Namrata ChhabraBiochemistry for Medics- Lecture noteswww.namrata.co

04/13/23 1Biochemistry for medics- Lecture notes

• The ability to utilize carbohydrates can be determined by Glucose tolerance test.

• Initially fasting blood glucose is estimated• A loading dose of glucose is given.• The blood glucose levels are estimated at

regular intervals after the glucose load• In conditions of insulin deficiency, blood

glucose levels get elevated due to impaired utilization of glucose.

04/13/23 2Biochemistry for medics- Lecture notes

A) Decreased Glucose toleranceDecreased carbohydrate tolerance

(non-utilization of carbohydrate load) is observed in conditions causing hyperglycemia, for example:

Diabetes mellitus Hyperactivity of anterior pituitary

and adrenal cortex Hyperthyroidism Stress04/13/23 3Biochemistry for medics- Lecture notes

B) Increased Glucose ToleranceIncreased carbohydrate tolerance is

observed in all conditions that cause hypoglycemia-

i) Hypopituitarism ii) Hyperinsulinism iii) Hypothyroidism iv) Adrenal cortical hypofunction v) Decreased gastro intestinal absorption

like sprue, celiac disease. 04/13/23 4Biochemistry for medics- Lecture notes

i) In asymptomatic persons with sustained or transient glycosuria

ii) In persons with symptoms of diabetes but no glycosuria or hyperglycemia

iii) Persons with family history but no symptoms or positive blood findings

04/13/23 5Biochemistry for medics- Lecture notes

iv)In persons with or without symptoms of diabetes mellitus showing one abnormal blood finding

v) In patients with neuropathies or retinopathies of unknown origin

vi) In women with H/o having delivered large babies.

04/13/23 6Biochemistry for medics- Lecture notes

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) The test should not be carried out in acutely ill patients

04/13/23 7Biochemistry for medics- Lecture notes

a) The patient is instructed to have good carbohydrate diet for 3 days prior to the test. Further , diet containing about 30-50 G of carbohydrate should be taken on the evening prior to the test.

b) The patient should avoid drugs likely to influence the blood glucose levels, for at least, 2 days prior to the test

04/13/23 8Biochemistry for medics- Lecture notes

c) Patient should abstain from smoking during the test.

d) Strenuous exercise on the previous day is to be avoided.

e) The exercise is also to be avoided on the same day prior to the test

04/13/23 9Biochemistry for medics- Lecture notes

Standard Oral glucose tolerance test

I/V Glucose tolerance test

Mini Glucose tolerance test

04/13/23 10Biochemistry for medics- Lecture notes

a) At about 8 a.m. the fasting blood and urine samples are collected. These are called zero samples.

b) A loading dose of 75 g. anhydrous glucose dissolved in 250-300 ml of water is given to the patient.

04/13/23 11Biochemistry for medics- Lecture notes

• In children 1.75 g of glucose /kg body weight is given.

• In the classical procedures, the blood and urine samples are collected at half hourly interval of the next two and a half hour or three hours.

• Glucose is estimated in all the blood samples.

• Urine is analyzed for the presence of glucose.

04/13/23 12Biochemistry for medics- Lecture notes

A curve is plotted with the blood glucose levels on the vertical axis against the time of collection on the horizontal axis.

The curve so obtained is called glucose tolerance curve.

04/13/23 13Biochemistry for medics- Lecture notes

Fasting (Zero sample)

30 minutes

60 minutes

90 minutes

120 minutes

150 minutes

180 minutes

Blood Glucose(mg/dl)

90 100 150 120 110 80 70

Urinary Glucose

nil nil nil nil nil nil nil

04/13/23 14Biochemistry for medics- Lecture notes

04/13/23 15Biochemistry for medics- Lecture notes

i) Fasting blood glucose (Zero hour sample)- is 90 mg /dl, which is well within the normal range(Normal 60-100 mg/dl).

ii) There is rise of blood glucose after glucose load and the peak value is observed at I hour. This is due to absorption of glucose from the intestine.

04/13/23 16Biochemistry for medics- Lecture notes

iii) Insulin is released upon increase of blood glucose level. There is fall in blood glucose with time due to glucose utilization promoted by insulin.

iv) The normal blood glucose level is achieved after 150 minutes.

04/13/23 17Biochemistry for medics- Lecture notes

1) Fasting blood glucose is higher than normal

2) The highest value is attained at 1 hour to 1 hour 30 minutes.

3) The highest value exceeds the renal threshold

4) Glucose is found in almost all the urine samples.

5) The blood glucose level does not return to the fasting level even within 2hour 30 minutes.

04/13/23 18Biochemistry for medics- Lecture notes

Fasting (Zero sample)

30 minutes

60 minutes

90 minutes

120 minutes

150 minutes

180 minutes

Blood Glucose(mg/dl)

200 225 350 300 275 250 225

Urinary Glucose

+ + + + + + +

04/13/23 19Biochemistry for medics- Lecture notes

Time in minutes

Blo

od g

luco

se (

mg/

Dl)

04/13/23 20Biochemistry for medics- Lecture notes

Blood glucose levels are within the normal limits.

Glucose tolerance curve is normal.There is lowering of renal threshold.Thus glucose is found in some of the

samples depending upon the renal threshold.

04/13/23 21Biochemistry for medics- Lecture notes

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.

04/13/23 22Biochemistry for medics- Lecture notes

Fasting (Zero sample)

30 minutes

60 minutes

90 minutes

120 minutes

150 minutes

180 minutes

Blood Glucose(mg/dl)

90 130 150 140 120 100 90

Urinary Glucose

nil + + + + ± nil

04/13/23 23Biochemistry for medics- Lecture notes

Time in minutes

Blo

od g

luco

se (

mg/

Dl)

04/13/23 24Biochemistry for medics- Lecture notes

Fasting blood glucose is normal.Sharp rise within 30 minutes to one

hourThe 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.

04/13/23 25Biochemistry for medics- Lecture notes

HyperthyroidismPregnancyAfter gastro-enterostomyEarly diabetes mellitus

04/13/23 26Biochemistry for medics- Lecture notes

Fasting (Zero sample)

30 minutes

60 minutes

90 minutes

120 minutes

150 minutes

180 minutes

Blood Glucose(mg/dl)

90 230 180 150 120 100 90

Urinary Glucose

nil + + nil nil nil nil

04/13/23 27Biochemistry for medics- Lecture notes

•This test is undertaken for patients with malabsorption (Celiac disease or enteropathies),•Under these conditions oral glucose load is not well absorbed and• the results of oral glucose tolerance test become inconclusive.

04/13/23 28Biochemistry for medics- Lecture notes

• I/V glucose tolerance test is carried out by giving 25 g of glucose dissolved in 100 ml distilled water as 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.

04/13/23 29Biochemistry for medics- Lecture notes

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.

04/13/23 30Biochemistry for medics- Lecture notes

a) Acute infections- Cortisol is secreted, the curve is elevated and prolonged

b) Liver diseases- The curve is elevated and prolonged.

c) Hyperthyroidism- There is steep rise in curve.

04/13/23 31Biochemistry for medics- Lecture notes

d) Hypothyroidism-A flat curve is obtained in hypothyroidism. Thyroid hormone increases the absorption of glucose from the gut.

e) Starvation- There is rise of counter regulatory hormones, which show increased glucose tolerance

04/13/23 32Biochemistry for medics- Lecture notes

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.

04/13/23 33Biochemistry for medics- Lecture notes

Time of sample collection

Normal person

Criteria for diagnosing diabetes mellitus

Criteria for diagnosing IGT

Fasting

<110 mg/dl <(6.1m.mol/L)

> 126 mg/dl >(7.0m.mol/L)

110- 126 mg/dl

2 hour after glucose load

<140 mg/dl <(7.8mmol/L)

> 200 mg/dl

140-199 mg/dl

04/13/23 34Biochemistry for medics- Lecture notes

For proper evaluation of the test, the subjects should be normally active and free from acute illness.

Medications that may impair glucose tolerance include diuretics, contraceptive drugs, glucocorticoids, niacin, and phenytoin should be avoided on that day.

04/13/23 35Biochemistry for medics- Lecture notes

Cortisone stress test- used for detecting pre diabetes or Latent diabetes

Extended GTT- To diagnose the cause of hypoglycemia especially 2-3 hours after meals.

04/13/23 36Biochemistry for medics- Lecture notes

If the fasting plasma glucose level is 126 mg/dL or higher on more than one occasion, further evaluation of the patient with a glucose challenge is unnecessary. However, when fasting plasma glucose is less than 126 mg/dL in suspected cases, a standardized oral glucose tolerance test may be done .

04/13/23 Biochemistry for medics- Lecture notes 37

A random plasma glucose concentration >11.1 mmol/L (200 mg/dL) accompanied by classic symptoms of DM (polyuria, polydipsia, weight loss) is sufficient for the diagnosis of DM.

04/13/23 Biochemistry for medics- Lecture notes 38