MLT GlobeOral glucose tolerance test, 2-hour (OGTT)
Diabetes · also called GTT, 75 g OGTT, 2-h PG
What it measures
The OGTT measures glucose before and 2 hours after drinking a standard glucose load. It diagnoses diabetes and impaired glucose tolerance and is the key test for gestational diabetes.
Specimen and preparation
- Specimen: Sodium fluoride plasma at 0 and 120 minutes (plus 60 minutes in pregnancy)
- Tube: Gray top
- Preparation: Normal carbohydrate diet for 3 days, 8–14 hour overnight fast, 75 g glucose drunk within 5 minutes; stay seated and do not smoke during the test.
Reference range
| Group | Range |
|---|---|
| Normal (2 h) | <140 (<7.8) mg/dL (mmol/L) |
| Impaired glucose tolerance (2 h) | 140–199 (7.8–11.0) mg/dL (mmol/L) |
| Diabetes (2 h) | ≥200 (≥11.1) mg/dL (mmol/L) |
| Gestational (IADPSG) any of | 0 h ≥92, 1 h ≥180, 2 h ≥153 mg/dL |
Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.
Causes of high values
- Diabetes or prediabetes
- Gestational diabetes
- Recent illness or bed rest
- Drugs (steroids, thiazides)
Causes of low values
- Malabsorption (flat curve)
- Reactive hypoglycaemia after gastric surgery
Method
Enzymatic glucose measurement on timed samples
Good to know
Do not perform if fasting glucose already confirms diabetes.
Related tests
📱 Practise with a timer, track your score and earn certificates in the free MLT Globe app – Google Play or practise online.