The diagnosis of diabetes is based upon symptoms and the results of blood tests.
Type 2 Diabetes Symptoms
Many patients diagnosed with diabetes have no diabetes symptoms at all, and are diagnosed by chance after a blood test.
Others have symptoms of hyperglycemia (high blood glucose) which include:
- Frequent urination.
- Increased thirst and hunger.
- Blurry vision (which improves after diagnosis and treatment for the high blood glucose).
Type 2 Diabetes Diagnosis
Testing for type 2 diabetes: Several blood tests are used to measure blood glucose (also called blood sugar) levels, the primary tests for diagnosing diabetes are:
- Random blood sugar test — For a random blood sugar test, you can have blood drawn at any time throughout the day, regardless of when you last ate.
- Fasting blood sugar test — A fasting blood sugar is a blood test done after not eating or drinking for 8 to 12 hours (usually overnight).
- Hemoglobin A1c test (HbA1c) — This test measures the average blood sugar level during the past two to three months. Normal values for HbA1c are 4 to 6 percent. The HbA1c test can be done at any time of day (before or after eating).
- Oral glucose tolerance test — Oral glucose tolerance testing (OGTT) is a test that involves drinking a specially formulated glucose solution (usually orange or cola flavored). Your blood sugar level is tested before you drink the solution, and then one and two hours after drinking it. This test is used for screening pregnant women for gestational diabetes.
Criteria for diagnosis
The following criteria are used to classify blood glucose levels as normal, pre-diabetes, or diabetes.
Normal – Fasting (first sugar of the morning) blood sugar less than 100 mg/dL (5.55 mmol/L).
Pre-diabetes – At least 50 percent of people with impaired glucose tolerance eventually develop type 2 diabetes, and there is an increased risk of heart disease even if diabetes does not develop. Impaired glucose tolerance is very common; about 11 percent of all people between the ages of 20 and 74 years have impaired glucose tolerance.
- Impaired fasting glucose is defined as a fasting blood sugar level between 100 and 125 mg/dL (5.6 to 6.9 mmol/L).
- Impaired glucose tolerance is defined as a blood sugar level of 140 to 199 mg/dL two hours after an oral glucose tolerance test.
Type 2 Diabetes — A person is considered to be diabetic if he or she has one or more of the following:
- Symptoms of diabetes and a random blood sugar of 200 mg/dL (11.1 mmol/L) or higher
- A fasting blood sugar level of 126 mg/dL (7.0 mmol/L) or higher
- A blood sugar of 200 mg/dL (11.1 mmol/L) or higher two hours after a 75 gram oral glucose tolerance test.
- A HbA1c of 6.5 percent or higher
- All of these blood tests must be repeated to confirm that the results remain abnormally high.
Read more about type 2 diabetes:
Reviewed by Dr. Mariela Glandt, Dec. 2013