Fasting blood sugarFBS, Fasting plasma glucoseFasting blood sugar is the glucose level in blood after at least eight hours without food or sweetened drink. It is the simplest and cheapest test for diabetes, and one of the three that can diagnose it.
Oral glucose tolerance test
Also known as OGTT, Glucose tolerance test, GTT
A test where you drink a measured sugary solution and have your blood sugar checked two hours later, to see how well your body clears it.
You arrive fasting, give a blood sample, drink a solution containing 75 grams of , and give another sample two hours later.
What the two-hour result means
| Result | Meaning |
|---|---|
| Below 140 mg/dL | Normal |
| 140–199 mg/dL | Prediabetes (impaired glucose tolerance) |
| 200 mg/dL or above | Diabetes range — confirm with a repeat test |
It is more sensitive than a fasting sample alone, which is why it is the standard test for in pregnancy.
Related terms
- HbA1cGlycated haemoglobin, A1cHbA1c measures the proportion of haemoglobin that has sugar stuck to it, which reflects the average blood glucose over roughly the past three months. It needs no fasting and is used both to diagnose diabetes and to judge how well it is controlled.
- PrediabetesBorderline diabetes, Impaired glucose toleranceBlood sugar that is higher than normal but not yet high enough to be called diabetes. It usually causes no symptoms at all, and it can often be reversed.
- Gestational diabetesGDM, Diabetes in pregnancyDiabetes that appears during pregnancy in a woman who did not have it before. It usually resolves after delivery but raises the risk of type 2 diabetes later.