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Tests and diagnosis

By Mayo Clinic staff

Tests for type 1 and type 2 diabetes
In 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 1 and 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 works by measuring 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.

If the A1C test isn't available, or if you have certain conditions that can make the A1C test inaccurate — such as if you're pregnant or have an uncommon form of hemoglobin (known as a hemoglobin variant) — your doctor may use the following tests to diagnose diabetes:

  • Random blood sugar test. A blood sample will be taken at a random time. Regardless of when you last ate, a random blood sugar level of 200 milligrams per deciliter (mg/dL) — 11.1 millimoles per liter (mmol/L) — or higher suggests diabetes.
  • Fasting blood sugar test. A blood sample will be taken after an overnight fast. A fasting blood sugar level between 70 and 99 mg/dL (3.9 and 5.5 mmol/L) is normal. If it's 126 mg/dL (7 mmol/L) or higher on two separate tests, you'll be diagnosed with diabetes.

Tests for gestational diabetes
Screening for gestational diabetes is a routine part of prenatal care. Most health care providers recommend a blood test known as a glucose challenge test between the 24th and 28th weeks of pregnancy — or earlier if you're at particularly high risk of gestational diabetes.

You'll begin the glucose challenge test by drinking a syrupy glucose solution. One hour later, you'll have a blood test to measure your blood sugar level. A blood sugar level above 140 mg/dL (7.8 mmol/L) usually indicates gestational diabetes, but you'll likely need a second test to confirm the diagnosis.

For the follow-up test, you'll be asked to fast overnight. Then you'll drink another sweet solution — this one containing a higher concentration of glucose — and your blood sugar level will be checked every hour for a period of three hours.

Tests for prediabetes
The American College of Endocrinology suggests prediabetes testing for anyone who has a family history of type 2 diabetes and for those who are obese or have metabolic syndrome. Women with a personal history of gestational diabetes also should be tested.

The primary test to screen for prediabetes is the:

  • Glycated hemoglobin (A1C) test. This blood test indicates your average blood sugar level for the past two to three months. It works by measuring 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 between 6 and 6.5 percent suggests you have prediabetes.

If the A1C test isn't available, or if you have certain conditions that can make the A1C test inaccurate — such as if you're pregnant or have an uncommon form of hemoglobin (known as a hemoglobin variant) — your doctor may use the following tests to diagnose diabetes:

  • Fasting blood sugar test. A blood sample will be taken after an overnight fast. A blood sugar level from 100 to 125 mg/dL (5.6 to 6.9 mmol/L) is considered prediabetes.
  • Oral glucose tolerance test. A blood sample will be taken after you fast for at least eight hours or overnight. Then you'll drink a sugary solution, and your blood sugar level will be measured again after two hours. A blood sugar level less than 140 mg/dL (7.8 mmol/L) is normal. A blood sugar level from 140 to 199 mg/dL (7.8 to 11 mmol/L) is considered prediabetes. This is sometimes referred to as impaired glucose tolerance (IGT). A blood sugar level of 200 mg/dL (11.1 mmol/L) or higher may indicate diabetes.
Treatments and drugs Preparing for your appointment
References
  1. All about diabetes. American Diabetes Association. http://www.diabetes.org/about-diabetes.jsp. Accessed Dec. 25, 2008.
  2. Collazo-Clavell ML, ed. The Essential Diabetes Guide. Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2008.
  3. Diagnosis and management of type 2 diabetes mellitus in adults. Bloomington, Minn.: Institute for Clinical Systems Improvement. http://www.icsi.org/diabetes_mellitus__type_2/management_of_type_2_diabetes_mellitus__9.html. Accessed Jan. 1, 2009.
  4. Gastroparesis: What you should know. American Academy of Family Physicians. www.aafp.org/afp/20080615/1703ph.html. Accessed Jan. 1, 2009.
  5. McCulloch DK. Overview of medical care in adults with diabetes mellitus. http://www.uptodate.com/home/index.html. Accessed Jan. 1, 2009.
  6. Your guide to diabetes: Type 1 and type 2. National Diabetes Information Clearinghouse. http://diabetes.niddk.nih.gov/dm/pubs/type1and2/YourGuide2Diabetes.pdf. Accessed Jan. 1, 2009.
  7. Diabetes in pregnancy. March of Dimes. http://search.marchofdimes.com/cgi-bin/MsmGo.exe?grab_id=6&page_id=12648448&query=gestational+diabetes&hiword=DIABETIC+GESTATION+GESTATIONS+diabetes+gestational+. Accessed Jan. 29, 2009.
  8. Gestational diabetes. American Diabetes Association. http://www.diabetes.org/gestational-diabetes.jsp. Accessed Jan. 1, 2009.
  9. Am I at risk for type 2 diabetes? National Diabetes Information Clearinghouse. http://diabetes.niddk.nih.gov/dm/pubs/riskfortype2/risk.pdf. Accessed Jan. 1, 2009.
  10. Eisenbarth GS, et al. Type 1 diabetes mellitus. In: Kronenberg HM, et al. Williams Textbook of Endocrinology. 11th ed. Philadelphia, Pa.: Saunders Elsevier; 2008. http://www.mdconsult.com/das/book/body/115481400-2/0/1555/195.html#4-u1.0-B978-1-4160-2911-3..50033-9--p1391. Accessed Jan. 1, 2009.
  11. Diabetes and pregnancy. American College of Obstetricians and Gynecologists. http://www.acog.org/publications/patient_education/bp051.cfm. Accessed Jan. 1, 2009.
  12. Managing gestational diabetes. National Institute of Child Health and Human Development. http://www.nichd.nih.gov/publications/pubs/gest_diabetes/. Accessed Jan. 1, 2009.
  13. Am I at risk for gestational diabetes? National Institute of Child Health and Human Development. http://www.nichd.nih.gov/publications/pubs/upload/gest_diabetes_risk_2005.pdf. Accessed Jan. 1, 2009.
  14. Diabetes. In: Williams Obstetrics. 22nd ed. New York, N.Y.: McGraw-Hill; 2005. http://www.accessmedicine.com/content.. aspx?aID=738493. Accessed Jan. 1, 2009.
  15. Pancreas transplantation. American Diabetes Association. http://www.diabetes.org/type-1-diabetes/pancreas-transplants.jsp. Accessed Jan. 1, 2009.
  16. Other diabetes medications. American Diabetes Association. http://www.diabetes.org/type-2-diabetes/oral-medications.jsp. Accessed Jan. 1, 2009.
  17. Tetanus disease in-short (Lockjaw). Centers for Disease Control and Prevention. http://www.cdc.gov/vaccines/vpd-vac/tetanus/in-short-both.htm. Accessed Jan. 1, 2009.
  18. Smoking. American Diabetes Association. http://www.diabetes.org/type-1-diabetes/smoking.jsp. Accessed Jan. 1, 2009.
  19. Eye complications. American Diabetes Association. http://www.diabetes.org/type-2-diabetes/eye-complications.jsp. Accessed Jan. 6, 2009.
  20. Saller A, et al. Diabetes and osteoporosis. Aging Clinical and Experimental Research. 2008;20:280.
  21. American College of Endocrinology: Task Force on Prediabetes. American College of Endocrinology consensus statement on the diagnosis and management of pre-diabetes in the continuum of hyperglycemia - When do the risks of diabetes begin? http://www.aace.com/meetings/consensus/hyperglycemia/hyperglycemia.pdf. Accessed Jan. 9, 2009.
  22. International Expert Committee. International Expert Committee report on the role of the A1C assay in the diagnosis of diabetes. Diabetes Care. 2009;32:1.

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June 13, 2009

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