Which condition will lead to erroneous results in an oral glucose tolerance test (OGTT)?

• A. No Food, Coffee, Tea, or Smoking 8 Hours Before and During the Test
• B. Ambulatory 3 Days Prior to Testing
• C. Administration of 75 g of Glucose After a 10-12 Hour Fast
• D. Carbohydrate Restriction to Below 150 g/day for 3 Days Prior

Answer: (D)

Carbohydrate intake in the days before an OGTT must be normal to ensure the glucose response reflects typical daily metabolism. When carbohydrate consumption is restricted to below about 150 g/day for several days, the body’s glucose handling changes enough that the post-load glucose excursion during the test can be misleading—often producing a lower or atypical result that does not represent the patient’s usual glucose tolerance. This makes the test unreliable for diagnosing diabetes or impaired glucose tolerance. Maintaining a normal carbohydrate intake (about 150 g/day) for several days before the test helps preserve accuracy. In contrast, fasting overnight, avoiding food or stimulants as instructed, and giving the standard 75 g glucose load after the fast are appropriate conditions that support valid results.