Glucose Challenge Tests
Two hour postprandial serum glucose
After an overnight fast (8-12 hours), draw a specimen for fasting serum glucose. The patient is then given a breakfast containing 100 grams of carbohydrate. Two hours later, a single sample of blood is drawn into a red top or grey top (NaF) tube for glucose determination.
Oral Glucose tolerance tests
Indications: In adults, the presence of diabetic symptoms with unequivocal hyperglycemia, or fasting plasma glucose levels greater than 140 mg/dl on more than one occasion, is diagnostic of diabetes mellitus, and an oral glucose tolerance test is not required for diagnosis. In children, the presence of classic symptoms of diabetes together with a random plasma glucose > 200 mg/dl is diagnostic, and an oral glucose tolerance test is not required for diagnosis in this case.
The oral glucose tolerance test is indicated on patients where there is a clinical impression of possible diabetes
a. Oral Glucose Tolerance Test - In Non-Pregnant Adults and Children
Patient Preparation: The oral glucose tolerance test should be performed after 3 days of an unrestricted diet containing a minimum of 150 grams of carbohydrates daily and of unrestricted physical activity. The patient should have fasted for 8-12 hours (overnight) but not more than 16 hours. Water is permitted during this period.
During the test, the patient should remain seated and refrain from smoking.
Specimen collection requirements: All blood specimens should be collected in a grey top (fluoride) tube, labeled with the time, and sent to the laboratory as drawn. Red tops are acceptable but be aware that specimens allowed to stand at room temperature may show a false decrease in glucose levels. Venous blood samples are preferable.
Dosage: In adults, 75 grams of glucose is administered. In children, 1.75 g/kg of ideal body weight up to 75 grams is administered. The glucose dose concentration should not exceed 25 g/dl.
Procedure: A fasting blood sample is collected. The glucose dose is given and should be drunk in 5 minutes. Time zero is the beginning of the drink, and blood samples are drawn according to the ordered protocol.
b. Oral Glucose Tolerance Test During Pregnancy:
Preparations and specimen collection: Same as above.
Dosage: 100 grams of glucose is administered in a concentration not to exceed 25 g/dl.
Procedure: A fasting blood sample is collected. 100 grams of glucose is given over a 5 minute interval. Time zero is the beginning of the drink. Blood samples are drawn at 1hr, 2 hrs, and 3 hrs.