Glucose tolerance test

Alternative names:

GTT; OGTT; oral glucose tolerance test

Normal values:

blood:

• fasting: 70 to 115 mg/dl
• 30 min.: less than 200
• 1 hour: less than 200
• 2 hour: less than 140
• 3 hour: 70 to 115
• 4 hour: 70 to 115

urine:

• negative (no glucose present)

Note: mg/dl = milligrams per deciliter

What abnormal results mean:

Greater-than-normal levels of glucose may indicate

• Cushing's syndrome
• diabetes mellitus
• gestational diabetes

Abnormal results could also indicate:

• hypoglycemia

Additional conditions under which the test may be performed:

• dementia due to metabolic causes
• glucagonoma
• insulin-dependent diabetes mellitus (IDDM)
• islet of Langerhans' tumor
• nephrotic syndrome