Lab test · Metabolic
Oral glucose tolerance test (OGTT)
An oral glucose tolerance test measures how the body handles a sugar drink over two hours. When it is used to diagnose prediabetes and diabetes and how to prepare.
Written by LON6EVITY Editorial Team · Last updated
How it works
After fasting, blood glucose is measured, you drink a standard glucose solution, and glucose is measured again — usually after two hours. MedlinePlus describes the procedure.
What it is used for
NIDDK lists the OGTT alongside fasting glucose and HbA1c as tests for diagnosing prediabetes and diabetes. It is also used, in a different format, to check for gestational diabetes in pregnancy.
Preparation
Follow the fasting instructions and keep eating normally in the days before, since very low carbohydrate intake can affect the result. Illness and some medicines also influence it.
Factors that can affect the result
- Fasting
- Recent diet
- Illness
- Medicines
- Pregnancy
Questions people commonly ask
- Why use an OGTT if HbA1c exists?
- It can detect abnormal glucose handling after eating that fasting glucose or HbA1c may miss, and it is standard in pregnancy.
Related biomarkers
Related topics
Keep your health results in one place
What does this mean for your own health data? Log your results, follow trends over time and bring an organised summary to your next doctor's appointment.
Sources
- Glucose tolerance test - non-pregnant. MedlinePlus, U.S. National Library of Medicine.
- Diabetes Tests & Diagnosis. National Institute of Diabetes and Digestive and Kidney Diseases (NIH).