Glucose Tolerance Test
A diagnostic test for diabetes and impaired glucose tolerance where blood glucose is measured before and after drinking a glucose solution. The oral glucose tolerance test (OGTT) is used to diagnose gestational diabetes and to assess glucose metabolism in clinical trials of metabolic peptide drugs.
Technical Context
75g OGTT protocol: overnight fast → fasting blood glucose → 75g anhydrous glucose dissolved in 300mL water consumed over 5 minutes → blood glucose at 1 hour (for GDM screening) and 2 hours. Diagnostic criteria (WHO/ADA): normal (2h glucose <140 mg/dL), impaired glucose tolerance (2h 140-199 mg/dL), diabetes mellitus (2h ≥200 mg/dL). For GDM (IADPSG criteria): fasting ≥92, 1h ≥180, 2h ≥153 mg/dL (any one value diagnostic). In acromegaly: 75g OGTT with serial GH measurements — failure to suppress GH below 1 μg/L (or 0.4 μg/L with ultrasensitive assays) confirms autonomous GH secretion. After treatment (surgery or somatostatin analogue), repeat OGTT assesses biochemical remission. The OGTT also has research applications in metabolic peptide drug trials: characterising glucose disposition (insulin sensitivity and beta cell function from OGTT-derived indices: Matsuda index, insulinogenic index, oral disposition index).