What is the recommended fasting duration before a 2-hour OGTT?

• A. 8-14 hours
• B. 2-4 hours
• C. 24 hours
• D. 0 hours

Answer: (A)

In an oral glucose tolerance test, a true fasting baseline is essential to prevent recent meals from biasing the starting glucose level and the subsequent 2-hour result. Fasting for about 8 to 14 hours—typically overnight—lets the body clear recent food influences, so the fasting glucose reflects baseline hepatic glucose production and insulin sensitivity rather than a postprandial spike. This standardization is what makes the 2-hour reading after the glucose load interpretable and reliable.

Fasting for only 2–4 hours would still leave recent digestion affecting the baseline, leading to an inaccurate starting point. Fasting for 24 hours is longer than needed and burdensome without improving accuracy. Not fasting at all would defeat the purpose of measuring a true fasting baseline. Water is usually allowed during the fasting period, but calories should be avoided.

So the recommended duration is 8–14 hours of fasting before a 2-hour OGTT.