Blood tests to diagnose diabetes

Although urine and fingerprick tests can reveal a higher than normal blood glucose level, you need one or more of three laboratory blood tests to diagnose diabetes; the random or fasting blood glucose test and, if necessary, the oral glucose tolerance test.

Random blood glucose test

A blood sample is taken from your arm for analysis by a laboratory. The sample can be taken whether or not you have eaten recently. Your health professional receives the results within a week.

What the results mean If you have symptoms and a test result above 200 mg/dl, you are diagnosed with diabetes. If you have no symptoms, or the result is less than this, you may be asked to repeat the test while fasting or to take an oral glucose tolerance test.

Fasting blood glucose test

You do not eat or drink overnight and a blood sample is taken in the morning. The sample is sent for analysis, and the results are available within a week.

What the results mean If you have symptoms and a test result above 126 mg/dl, you have diabetes. If you have no symptoms, or the result is less than this and you have symptoms, you may need to repeat the test or take an oral glucose tolerance test.

Oral glucose tolerance test

You do not eat or drink overnight. In the morning, a blood sample is taken immediately before and 2 hours after drinking a sugary drink. The samples are sent for analysis and the results are available within a week.

What the results mean If your fasting level is above 126 mg/dl and/or your 2-hour test result is above 200 mg/dl, you are diagnosed with diabetes, whether or not you have symptoms. This test is used when other tests have been inconclusive or to diagnose gestational (pregnancy-related) diabetes.