Free
E-newsletter
Subscribe to Housecall
Our weekly general interest
e-newsletter keeps you up to date
on a wide variety of health topics.
Mayo Clinic Housecall
Stay up to date on the latest health information.
What you get
- Free weekly e-newsletter
- Mayo Clinic expertise
- Recipes, tools and other helpful information
- We do not share your e-mail address
Tests and diagnosis
By Mayo Clinic staffIn June 2009, an international committee composed of experts from the American Diabetes Association, the European Association for the Study of Diabetes and the International Diabetes Federation recommended that type 2 diabetes testing include the:
- Glycated hemoglobin (A1C) test. This blood test indicates your average blood sugar level for the past two to three months. It measures the percentage of blood sugar attached to hemoglobin, the oxygen-carrying protein in red blood cells. The higher your blood sugar levels, the more hemoglobin you'll have with sugar attached. An A1C level of 6.5 percent or higher on two separate tests indicates you have diabetes. A result between 5.7 and 6.4 percent is considered prediabetes, which indicates a high risk of developing diabetes. Normal levels are below 5.7 percent.
If the A1C test isn't available, or if you have certain conditions — such as if you're pregnant or have an uncommon form of hemoglobin (known as a hemoglobin variant) — that can make the A1C test inaccurate, your doctor may use the following tests to diagnose diabetes:
- Random blood sugar test. A blood sample will be taken at a random time. Blood sugar values are expressed in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L). Regardless of when you last ate, a random blood sugar level of 200 mg/dL (11.1 mmol/L) or higher suggests diabetes, especially when coupled with any of the signs and symptoms of diabetes, such as frequent urination and extreme thirst. A level between 140 mg/dL (7.8 mmol/L) and 199 mg/dL (11.0 mmol/L) is considered prediabetes, which puts you at greater risk of developing diabetes. A blood sugar level less than 140 mg/dL (7.8 mmol/L) is normal.
- Fasting blood sugar test. A blood sample will be taken after an overnight fast. A fasting blood sugar level less than 100 mg/dL (5.6 mmol/L) is normal. A fasting blood sugar level from 100 to 125 mg/dL (5.6 to 6.9 mmol/L) is considered prediabetes. If it's 126 mg/dL (7 mmol/L) or higher on two separate tests, you have diabetes.
- Oral glucose tolerance test. For this test, which is rarely used anymore, you fast overnight, and the fasting blood sugar level is measured. Then you drink a sugary liquid, and blood sugar levels are tested periodically for the next two hours. A blood sugar level less than 140 mg/dL (7.8 mmol/L) is normal. A reading of more than 200 mg/dL (11.1 mmol/L) after two hours indicates diabetes. A reading between 140 and 199 mg/dL (7.8 mmol/L and 11.0 mmol/L) indicates prediabetes.
The American Diabetes Association recommends routine screening for type 2 diabetes beginning at age 45, especially if you're overweight. If the results are normal, repeat the test every three years. If the results are borderline, ask your doctor when to come back for another test. Screening is also recommended for people who are under 45 and overweight if there are other heart disease or diabetes risk factors present, such as a sedentary lifestyle, a family history of type 2 diabetes, a personal history of gestational diabetes or blood pressure above 135/80 millimeters of mercury (mm Hg).
If you're diagnosed with diabetes, the doctor may do other tests to distinguish between type 1 and type 2 diabetes — which often require different treatments.
After the diagnosis
A1C levels need to be checked between two and four times a year. Your target A1C goal may vary depending on your age and other factors. However, for most people, the American Diabetes Association recommends an A1C level below 7 percent. Ask your doctor what your A1C target is.
The American Diabetes Association has a formula that translates the A1C into what's known as an estimated average glucose (eAG). The eAG more closely correlates with daily blood sugar readings. An A1C of 7 percent translates to an eAG of 154 mg/dL (8.5 mmol/L).
Compared with repeated daily blood sugar tests, A1C testing better indicates how well your diabetes treatment plan is working. An elevated A1C level may signal the need for a change in your medication or meal plan.
In addition to the A1C test, the doctor will take blood and urine samples periodically to check your cholesterol levels, thyroid function, liver function and kidney function. The doctor will also assess your blood pressure. Regular eye and foot exams also are important.
- Longo DL, et al. Harrison's Online. 18th ed. New York, N.Y.: The McGraw-Hill Companies; 2012. http://www.accessmedicine.com/resourceTOC.aspx?resourceID=4. Accessed Sept. 23, 2012.
- Diabetes mellitus (DM). The Merck Manuals: The Merck Manual for Healthcare Professionals. http://www.merck.com/mmpe/sec12/ch158/ch158b.html#sec12-ch158-ch158b-1105. Accessed Sept. 30, 2012.
- Inzucchi SE, et al. Management of hyperglycemia in type 2 diabetes: A patient-centered approach. Diabetes Care. 2012;35:1364.
- Standards of medical care in diabetes — 2013. Diabetes Care. 2013:36:S1.
- Bonoro E, et al. The pros and cons of diagnosing diabetes with A1C. Diabetes Care. 2011;34:S184.
- Your guide to diabetes: Type 1 and type 2. National Institute of Diabetes and Digestive and Kidney Diseases. http://diabetes.niddk.nih.gov/dm/pubs/type1and2/index.htm. Accessed Sept. 23, 2012.
- Screening for type 2 diabetes mellitus in adults. U.S. Preventive Services Task Force. http://www.uspreventiveservicestaskforce.org/uspstf08/type2/type2rs.htm. Accessed Sept. 23, 2012.
- Diabetes statistics. American Diabetes Association. http://www.diabetes.org/diabetes-basics/diabetes-statistics. Accessed Sept. 23, 2012.
- What people with diabetes need to know about osteoporosis. National Institute of Arthritis and Musculoskeletal and Skin Diseases. http://www.niams.nih.gov/Health_Info/Bone/Osteoporosis/Conditions_Behaviors/diabetes.asp. Sept. 23, 2011.
- Mazzola N. Review of current and emerging therapies in type 2 diabetes mellitus. American Journal of Managed Care. 2012;18:S17.
- Take charge of your diabetes. Centers for Disease Control and Prevention. http://www.cdc.gov/diabetes/pubs/tcyd/vaccin.htm. Accessed Sept. 30, 2012.
- Hyperosmolar hyperglycemic nonketotic syndrome (HHNS). American Diabetes Association. http://www.diabetes.org/living-with-diabetes/complications/hyperosmolar-hyperglycemic.html. Accessed Sept. 19, 2012.
- Dixon JB, et al. Bariatric surgery: An IDF statement for obese type 2 diabetes. Arquivos Brasileiros de Endocrinologia & Metabologia. 2011;55:367.
- Before pregnancy. American Diabetes Association. http://www.diabetes.org/living-with-diabetes/complications/pregnant-women/before-pregnancy.html. Accessed Sept. 30, 2012.
- Helzner EP, et al. Contribution of vascular risk factors to the progression in Alzheimer disease. Archives of Neurology. 2009;66:343.
- Bainbridge KE. Diabetes and hearing impairment in the United States: Audiometric evidence from the National Health and Nutrition Examination Survey, 1999 to 2004. Annals of Internal Medicine. 2008;149:1.
- Schauer PR, et al. Bariatric surgery vs. intense medical therapy in obese patients with diabetes. New England Journal of Medicine. 2012;366:1567.
- Mingrone G, et al. Bariatric surgery vs. conventional medical therapy for type 2 diabetes. New England Journal of Medicine. 2012;366:1577.
- A1C. American Diabetes Association. http://www.diabetes.org/living-with-diabetes/treatment-and-care/blood-glucose-control/a1c/?keymatch=a1c. Accessed Oct. 1, 2012.
Find Mayo Clinic on