Diagnostic tests include:
- 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 the oxygen-carrying protein in red blood cells (hemoglobin). 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 diabetes.
If the A1C test isn't available, or if you have certain conditions that can make the A1C test inaccurate — such as pregnancy or an uncommon form of hemoglobin (hemoglobin variant) — your doctor may use these tests:
- Random blood sugar test. A blood sample will be taken at a random time and may be confirmed by repeat testing. 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.
- 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.
If you're diagnosed with diabetes, your doctor may also run blood tests to check for autoantibodies that are common in type 1 diabetes. These tests help your doctor distinguish between type 1 and type 2 diabetes when the diagnosis is uncertain. The presence of ketones — byproducts from the breakdown of fat — in your urine also suggests type 1 diabetes, rather than type 2.
After the diagnosis
You'll regularly visit your doctor to discuss diabetes management. During these visits, the doctor will check your A1C levels. Your target A1C goal may vary depending on your age and various other factors, but the American Diabetes Association generally recommends that A1C levels be below 7 percent, which translates to an estimated average glucose 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 insulin regimen, meal plan or both.
In addition to the A1C test, the doctor will also take blood and urine samples periodically to check your cholesterol levels, thyroid function, liver function and kidney function. The doctor will also examine you to assess your blood pressure and will check the sites where you test your blood sugar and deliver insulin.
Aug. 07, 2017
- Standards of medical care in diabetes — 2017: Summary of revisions. Diabetes Care. 2017;40(suppl):S5.
- Papadakis MA, et al., eds. Diabetes mellitus & hypoglycemia. In: Current Medical Diagnosis & Treatment 2017. 56th ed. New York, N.Y.: McGraw-Hill Education; 2017. http://accessmedicine.mhmedical.com. Accessed April 19, 2017.
- What is diabetes? National Institute of Diabetes and Digestive and Kidney Diseases. https://www.niddk.nih.gov/health-information/diabetes/overview/what-is-diabetes. Accessed April 19, 2017.
- Levitsky LL, et al. Epidemiology, presentation, and diagnosis of type 1 diabetes mellitus in children and adolescents. https://www.uptodate.com/home. Accessed April 19, 2017.
- Diabetes mellitus (DM). Merck Manual Professional Version. http://www.merckmanuals.com/professional/endocrine_and_metabolic_disorders/diabetes_mellitus_and_disorders_of_carbohydrate_metabolism/diabetes_mellitus_dm.html. Accessed April 19, 2017.
- AskMayoExpert. Type 1 diabetes mellitus. Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2015.
- Robertson RP, et al. Pancreas and islet transplantation in diabetes mellitus. https://www.uptodate.com/home. Accessed April 21, 2017.
- Levitsky LL, et al. Special situations in children and adolescents with type 1 diabetes mellitus. https://www.uptodate.com/home. Accessed April 19, 2017.
- Hyperglycemia (High blood glucose). American Diabetes Association. http://www.diabetes.org/living-with-diabetes/treatment-and-care/blood-glucose-control/hyperglycemia.html. Accessed April 19, 2017.
- DKA (ketoacidosis) and ketones. American Diabetes Association. http://www.diabetes.org/living-with-diabetes/complications/ketoacidosis-dka.html. Accessed April 19, 2017.
- Prediabetes & insulin resistance. National Institute of Diabetes and Digestive and Kidney Diseases. https://www.niddk.nih.gov/health-information/diabetes/overview/what-is-diabetes/prediabetes-insulin-resistance. Accessed April 19, 2017.
- About insulin and high blood glucose. American Diabetes Association. http://www.diabetes.org/are-you-at-risk/lower-your-risk/highbg.html. Accessed April 19, 2017.
- McCulloch DK, et al. Glycemic control and vascular complications in type 1 diabetes. https://www.uptodate.com/home. Accessed April 20, 2017.
- Diabetes and oral health problems. American Diabetes Association. http://www.diabetes.org/living-with-diabetes/treatment-and-care/oral-health-and-hygiene/diabetes-and-oral-health.html. Accessed April 20, 2017.
- Drug treatment of diabetes mellitus. Merck Manual Professional Version. http://www.merckmanuals.com/professional/endocrine-and-metabolic-disorders/diabetes-mellitus-and-disorders-of-carbohydrate-metabolism/drug-treatment-of-diabetes-mellitus. Accessed April 21, 2017.
- McCulloch DK, et al. Management of blood glucose in adults with type 1 diabetes mellitus. https://www.uptodate.com/home. Accessed April 21, 2017.
- FDA proves first automated insulin delivery device for type 1 diabetes. U.S. Food and Drug Administration. https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm522974.htm. Accessed April 21, 2017.
- Forlena GP. Insulin infusion sets and continuous glucose monitoring sensors: Where the artificial pancreas meets the patient. Diabetes Technology and Therapeutics. 2017;19:206.
- Hypoglycemia. American Diabetes Association. http://professional.diabetes.org/pel/hypoglycemia-english. Accessed April 21, 2017.
- Questions & answers about diabetes in the workplace and the Americans with disabilities act. U.S. Equal Opportunity Employment Commission. https://www.eeoc.gov/laws/types/diabetes.cfm. Accessed April 21, 2017.
- Castro MR (expert opinion). Mayo Clinic, Rochester, Minn. May 9, 2017.