The doctor will ask about your symptoms and medical and family history. A physical exam will be done. There are four main tests used to diagnose diabetes. Most tests results should be confirmed with repeat testing. The American Diabetes Association (ADA) recommends using one of the following tests to make the diagnosis:
Fasting Plasma Glucose Test
You will need to avoid eating for at least 8 hours before the test. A sample of your blood will be taken. The blood glucose level will be measured. A measure of 126 milligrams per deciliter (mg/dl) (7 millimole per liter of blood [mmol/L]) or higher indicates a diagnosis of diabetes.
Random Plasma Glucose Test
Symptoms typical of diabetes include excessive thirst and hunger, frequent urination, and weight loss. Your doctor will make the diagnosis based on your symptoms and the results of the random plasma glucose test. This test is taken any time of day (without regard to when you have last eaten). A sample of your blood will be taken. The blood glucose level will be measured. A measure of 200 (mg/dl) [11.1 mmol/L] or higher along with typical symptoms indicates the presence of diabetes.
Two-hour Glucose Tolerance Test
This starts with a 3-day intake of a diet consisting of at least 150 grams of carbohydrates. You will then be asked to fast overnight (between 8-16 hours). The test is generally done in the morning, in your doctor's office.
A blood sample will be obtained from you to measure the blood sugar level. Then, you will drink 75 grams of glucose dissolved in water. Two hours later, another blood sample will be obtained to measure the blood sugar level. If you have diabetes, your blood sugar level will rise higher than normal and remain high for a much longer time than is normal. A measure of 200 mg/dl (11.1 mmol/L) or higher at 2 hours is considered a positive test.
Hemoglobin A1c (HbA1c)
The HbA1c test is a good indicator of your average blood sugar levels over the previous 2-4 months. This test usually does not require any dietary restrictions. A blood sample will be taken. If your HbA1c level is 6.5% or higher, this indicates a diagnosis of diabetes.
Other Commonly Ordered Tests
After the diagnosis of diabetes is confirmed, your doctor will most likely order the following tests:
- Urine microalbumin to see if there is any damage to your kidneys
- Blood lipids levels, such as total cholesterol levels, low-density lipoprotein (LDL) cholesterol levels, high-density lipoprotein (HDL) cholesterol levels, and triglycerides levels
- Kidney function tests, including serum creatinine; blood urea nitrogen (BUN); and potassium
- Reviewer: Kim A. Carmichael, MD, FACP
- Review Date: 09/2014 -
- Update Date: 09/17/2014 -