How is diabetes diagnosed?

Diabetes can be diagnosed with a blood test that measures the level of sugar (glucose) in the blood. Two different blood tests are available. One is called a "fasting plasma glucose" or FPG, which is the blood sugar level measured after fasting for eight hours.

Another test (the "2-hour plasma glucose" or 2-hr PG) measures blood sugar two hours after drinking a special sugar mixture.Test results are as follows:

  • Normal: FPG (fasting plasma glucose) level of less than 110 mg/dl (6.11 mmol/L) or 2-hr PG (2-hour plasma glucose) level of less than 140 mg/dl (7.78 mmol/L)
  • Borderline (high, but not enough for a diagnosis of diabetes): FPG (fasting plasma glucose) level of 110 to less than 126 mg/dl (6.11 to less than 7 mmol/L) or 2-hr PG (2-hour plasma glucose) level of 140 to less than 200 mg/dl (7.78 to less than 11.1 mmol/L)
  • High (suggests diabetes): FPG (fasting plasma glucose) level of 126 mg/dl or above (7 mmol/L or higher) or 2-hr PG (2-hour plasma glucose) level of 200 mg/dl or above (11.1 mmol/L or higher)

Diabetes can also be diagnosed if a patient has diabetes symptoms and a random blood sugar is 200 mg/dl or above (11.1 mmol/L or higher).

Errors can occur when screening for diabetes, and blood tests should be repeated at least once before the diagnosis is made.