There are several blood tests for prediabetes and diabetes.

Glycated hemoglobin (A1C) test

This test shows your average blood sugar level for the past three months.

In general:

  • NormalA1C level below 5.7
  • PrediabetesA1C level between 5.7 and 6.4
  • Type 2 DiabetesA1C level of 6.5 or higher on two separate tests

Certain conditions can make the A1C test inaccurate — such as if you’re pregnant or have an uncommon form of hemoglobin.

Fasting blood sugar test

A blood sample is taken after you fast for at least eight hours or overnight.

In general:

  • Normal – A fasting blood sugar level below 100 milligrams per deciliter (mg/dL) — 5.6 millimoles per liter (mmol/L)
  • Prediabetes – A fasting blood sugar level from 101 to 125 mg/dL (5.6 to 7.0 mmol/L). This result is sometimes called impaired fasting glucose.
  • Type 2 Diabetes – A fasting blood sugar level of 126 mg/dL (7.0 mmol/L) or higher.

Oral glucose tolerance test

This test is usually used to diagnose diabetes only during pregnancy. A blood sample is taken after you fast for at least eight hours or overnight. Then you’ll drink a sugary solution, and your blood sugar level will be measured again after two hours.

In general:

  • Normal – blood sugar level less than 140 mg/dL (7.8 mmol/L)
  • Prediabetes – blood sugar level from 140 to 199 mg/dL (7.8 to 11.0 mmol/L). This is sometimes referred to as impaired glucose tolerance.
  • Type 2 Diabetes – blood sugar level of 200 mg/dL (11.1 mmol/L) or higher.

If you have prediabetes, your doctor will typically check your blood sugar levels at least once a year.