Oral Glucose Tolerance Test By: Dr. Beenish Zaki Date: 09/05/2012 Senior Instructor Department of Biochemistry

Deficiency Of Insulin Relative or absolute deficiency of Insulin leads to diabetes. The gold standard of diagnosing diabetes in a patient is by performing an oral glucose tolerance test

Oral Glucose Tolerance Test The ability of a person to metabolize a given load of glucose is referred to as Oral Glucose Tolerance Test.

TERMINOLOGY For Adults : Fasting glucose:8-12 hours of fasting. Post parandial glucose: 2 hours after any meal. Renal Threshold: The concentration level up to which a substance such as glucose in the blood is prevented from passing through the kidneys into the urine Renal threshold for glucose is 180mg/dl

REFERENCE RANGE Unit NORMALIMPAIRED GLUCOSE TOLERANCE DIABETIC mmol/lmg/dlmmol/lmg/dlmmol/lmg/dl Fasting >7.0>125 Post Parandial <7.8< >11.0>200

Indications for OGTT Patients having no clinical symptoms with normal fasting and post lunch blood sugar but having glycosuria. Patients having symptoms suggestive of Diabetes Mellitus with normal blood sugar and urine sugar. Routinely carried out for all pregnant women especially for women who with excessive weight gain and a past history of having a big baby born weighing more than 4 kg or giving a history of repeated miscarriages.

Preparation of the patient Should be on a normal Carbohydrate diet (Approx.300 gms/ day) for at least 3 days prior to the test. If there is any infection treat it, avoid all the drugs 2 days prior to the test. Complete mental and physical rest. Abstain from smoking during the test. Not to take food after 8pm the previous night till 8am (12 hours called as post absorptive state) All sample of the blood should be venous.

Procedure: The patient is given a glucose load of 75gms (Adult) in a glass of water (Approx. 300ml).Pregnancy (100 gms) Fasting sample of venous blood is collected with urine for qualitative test for urine sugar and ketone bodies. A total of 6 specimens of venous blood and urine are collected every half an hour for a period of 2and half hours. A graph is plotted with the blood glucose value on the vertical axis and the time on the horizontal axis.

Normal Glucose Tolerance Test Sample Fasting ½ hr1 hr1 ½ hr2 hr2 ½ hr Blood Glucose Urine Glucose -ve Ketone Bodies -ve

Normal Glucose Tolerance Test Fasting blood glucose within normal limits of 60 to 100mg/dl. The highest peak value is reached within 1 hour. This is due to direct absorption of glucose from the intestine and increase insulin secretion and increased hepatic glycogenesis and decreased hepatic glycogenolysis. Highest value doesn’t exceed the renal threshold i.e. 180mg/dl By 2 ½ hours fasting level is reached again, this is due to increase glucose uptake utilization and storage in the tissues. No glucose and ketone bodies are detected in any specimen of urine.

Impaired Glucose Tolerance Test Sample Fasting ½ hr1 hr1 ½ hr2 hr2 ½ hr Blood Glucose Urine Glucose -ve +ve-ve Ketone Bodies -ve

Impaired Glucose Tolerance Test It is a condition where the glucose values are above the normal level but below the diabetic levels. In impaired glucose tolerance test FBS <125mg /dl and second hour blood glucose is <200mg/dl. Such persons need careful follow up because impaired glucose tolerance progresses to frank DM at the rate of 2% per year.

REFERENCE RANGE Unit NORMALIMPAIRED GLUCOSE TOLERANCE DIABETIC mmol/lmg/dlmmol/lmg/dlmmol/lmg/dl Fasting >7.0>125 Post Parandial <7.8< >11.0>200

Diabetic Glucose Tolerance Test Sample Fasting ½ hr1 hr1 ½ hr2 hr2 ½ hr Blood Glucose Urine Glucose +ve++ve+++ve++++ve+++ve++ve Ketone Bodies +ve

Diabetic Glucose Tolerance Test FBS is raised beyond 140mg/dl. Highest value is usually reached after 1 to 1 ½ hours which usually exceeds the renal threshold. Urine samples always contain glucose and ketone bodies depending upon the severity. Blood glucose does not return to normal level within 2 1/2 hours this is the most characteristic feature of Diabetes Mellitus

ADDITIONAL PARAMETER OGTT is to diagnose the disease, not to monitor everyday glucose levels. Fasting or random blood glucose is checked to look into control of diabetes. These values don’t indicate long term control of disease. Therefore the measurement of HbA1C, which is glucose modified hemoglobin. This gives the picture of long term glucose level-almost equal to the lifespan of RBC.

HbA1C Reference Range HbA1C Normal: % In the Case of Diabetics: <7% Good Control 7-8.5% Moderate Control >8.5% Poor Control

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