Glucose Tolerance Test
What is a glucose tolerance test?
The glucose tolerance test (GTT) is a timed series of blood glucose measurements taken after a glucose load is taken by the patient.
People with normal glucose metabolism will have a relatively modest rise in their blood sugar levels, whereas those with diabetes or impaired glucose tolerance will have a higher peak of their blood glucose levels.
When would you need a glucose tolerance test?
A GTT may be ordered by your doctor if they are suspicious of diabetes or impaired glucose tolerance, a milder form of disease which may occur before full-blown diabetes develops.
A single fasting or random blood glucose test may show a glucose level high enough to diagnose diabetes, but if there is doubt a glucose tolerance test may be needed.
Some women develop impaired glucose tolerance or gestational diabetes during pregnancy only, and a GTT is one way to detect this.
Symptoms of diabetes include:
- Excessive thirst leading to increased fluid intake (polydipsia)
- Frequent urination or increased urine output (polyuria)
- Weight loss or weight gain
- Frequent infections (skin infection, thrush etc.)
How is a glucose tolerance test performed?
The GTT is a blood test performed in the morning, after an 8 to 16 hour overnight fasting period. During this fasting period (at home), patients are not allowed to eat or drink, smoke, or exercise excessively.
The test takes 2 hours and is performed at the laboratory’s collection centre. Blood tests are taken at the beginning of the test and at regular intervals after a glucose-containing drink is taken.
Sometimes it is possible to take the blood samples from a small plastic tube left in the vein – an intravenous cannula.
Glucose tolerance test results explained
The GTT result will be forwarded to your doctor after several days. It may show:
- Normal test
- Impaired glucose tolerance – this is not diabetes, but may progress to diabetes; it usually requires a modification to the diet
- Diabetes mellitus – which may require diet control, oral medications, or insulin injections
- General Practitioner (GP)
- General Physician
- Occupational Health Physician
- General Surgeon
- Blood Test (venesection)
- Intravenous cannulation
- Pre-operative anaesthetic assessment
Also known as
- Oral glucose tolerance test
- Diabetes Australia
- Baker Institute (International Diabetes Institute)
- Wikipedia – Glucose Tolerance Test
This article is for informational purposes only and should not be taken as medical advice. If in doubt, HealthEngine recommends consulting with a registered health practitioner.