impaired glucose tolerance

Imagine giving the body a sugary drink and watching how quickly it clears the load. A healthy system mops up the glucose efficiently; one with impaired glucose tolerance is sluggish, leaving sugar lingering in the blood longer than it should. It is a stress test that reveals a control system beginning to lag, even when the resting (fasting) glucose still looks fine.

Impaired glucose tolerance is a category of prediabetes defined specifically by the result of an oral glucose tolerance test: a plasma glucose of 7.8–11.0 mmol/L (140–199 mg/dL) two hours after drinking a 75-gram glucose load, with a fasting level still below the diabetic range. It chiefly reflects insulin resistance in muscle plus a delayed or insufficient insulin response after meals.

IGT is distinct from impaired fasting glucose, which is identified from the fasting value alone; the two overlap but capture somewhat different defects, and a person can have one without the other. Like other forms of prediabetes, impaired glucose tolerance predicts progression to type 2 diabetes and elevated cardiovascular risk, and it responds well to weight loss and increased activity. The oral glucose tolerance test that detects it is more sensitive than fasting glucose but more cumbersome to perform.