Reading an oral glucose tolerance test curve
In a standard oral glucose tolerance test (OGTT), a person drinks 75 grams of glucose after an overnight fast, and blood glucose is sampled at intervals, classically fasting and at 2 hours. A typical insulin-sensitive response peaks within the first hour and returns toward baseline by 2 hours because circulating insulin moves glucose into muscle and fat efficiently.
An insulin-resistant pattern tends to show a higher peak, a delayed peak, and a slower fall, so the 2-hour value stays elevated. Diagnostic thresholds commonly cited are a 2-hour plasma glucose below 7.8 mmol/L (140 mg/dL) for normal tolerance, 7.8 to 11.0 mmol/L for impaired glucose tolerance, and 11.1 mmol/L (200 mg/dL) or above as one criterion for diabetes.
Why the shape matters more than a single number
The curve captures dynamics a single fasting reading misses. Two people can share a fasting glucose yet differ widely in how fast they clear a load, which reflects both insulin secretion and tissue insulin sensitivity. Researchers sometimes pair the glucose curve with insulin measurements to separate a secretion problem from a sensitivity problem.
Curve shapes vary with age, recent diet, illness, and activity, and a single test can be affected by these factors. This is general educational information, not a diagnosis; interpretation of any glucose test should be done by a qualified clinician using validated criteria.