Exams and Tests

Doctors use special tests in diagnosing diabetes and also in monitoring blood sugar level control in known diabetics.

If you are having symptoms but are not known to have diabetes, your evaluation should always begin with a thorough medical interview and physical examination. Your health care provider asks you about your symptoms, risk factors for diabetes, past medical problems, medications you are taking, allergies to medications, family history of diabetes or other medical problems such as high cholesterol or heart disease, and habits and lifestyle.

A number of lab tests are available to confirm the diagnosis of diabetes.

Fingerstick blood glucose: This is a rapid screening test that may be performed at a medical office or at a hospital emergency department.

• A fingerstick blood glucose test is not as accurate as testing your blood in the laboratory but is easy to perform, and the result is available right away.
  
  
• The test involves sticking your finger for a blood sample, which is then placed on a strip. The strip goes into a machine that reads the blood sugar level. These machines are only accurate to within about 10% of actual laboratory values.
  
  
• Fingerstick blood glucose values may be inaccurate at very high or very low levels, so this test is only a preliminary screening study. This is the way most diabetics monitor their blood sugar levels at home.

Fasting plasma glucose: You will be asked to eat or drink nothing for 8 hours before having your blood drawn (usually first thing in the morning). If the blood glucose level is greater than or equal to 126 mg/dL without eating anything, you probably have diabetes.

• If the result is abnormal, the fasting plasma glucose test may be repeated on a different day to confirm the result, or you may undergo an oral glucose tolerance test or a glycosylated hemoglobin test (often nicknamed "hemoglobin A1c") as a confirmatory test.
  
  
• If your fasting plasma glucose level is greater than 100 but less than 126 mg/dL, then you have what is called impaired fasting glucose or IFG. This is a prediabetes condition. You do not have diabetes, but you are at high risk of developing diabetes in the near future.

Oral glucose tolerance test: This test involves drawing blood for a fasting plasma glucose test and then drawing blood for a second test 2 hours after you drink a very sweet drink containing 75 grams of sugar.

• If the blood sugar level after the sugar drink is greater than or equal to 200 mg/dL, you are probably diabetic.
  
  
• If the blood glucose level is between 140 and 199, then you probably have impaired glucose tolerance, which is also a prediabetic condition.

Glycosylated hemoglobin or hemoglobin A1c: This test is a measurement of how high your blood sugar level has been over about the last 120 days—the lifespan of a red blood cell.

• Excess blood glucose hooks on to the hemoglobin in red blood cells and stays there for the life of the red blood cell, which is approximately 90 days.
  
  
• The percentage of hemoglobin that has had excess blood sugar attached to it can be measured in the blood. The test involves having a small amount of blood drawn.
  
  
• A hemoglobin A1c test is the best measurement of blood sugar control in people known to have diabetes. A hemoglobin A1c result of 7% or less is considered to indicate good glucose control. A result of 8% or greater is considered to indicate that your blood sugar level is too high too much of the time.
  
  
• The hemoglobin A1c test is also beginning to be used as a diagnostic test for diabetes. A hemoglobin A1c result greater than 6.1% is highly suggestive of diabetes. Generally, a confirmatory test would be needed before diagnosing diabetes.
  
  
• The hemoglobin A1c test is generally measured about every 3-6 months for people with known diabetes, although it may be done more frequently for people who are having difficulty achieving and maintaining good blood sugar control.
  
  
• This test is not used for people who do not have diabetes or are not at increased risk of diabetes.
  
  
• Normal values may vary from lab to lab, although an effort is under way to standardize how measurements are performed.

Diagnosing complications of diabetes

If you have diabetes, you should be checked regularly for early signs of diabetes complications. Your health care provider can do some of these checks; for others, you should be referred to a specialist.

• You should have your eyes checked at least once a year by an eye specialist (ophthalmologist) to screen for diabetic retinopathy, a leading cause of blindness.
  
  
• Your urine should be checked for protein (microalbumin) on a regular basis, at least 1-2 times per year. Protein in the urine is an early sign of diabetic nephropathy, a leading cause of kidney failure.
  
  
• Sensation in your legs should be checked regularly using a tuning fork or a monofilament device. Diabetic neuropathy is a leading cause in diabetic lower extremity ulcers, which frequently lead to amputation of the feet or legs.
  
  
• Your health care provider should check your feet and lower legs at every visit for cuts, scrapes, blisters, or other lesions that could become infected.
  
  
• You should be screened regularly for conditions that may contribute to heart disease, such as high blood pressure and high cholesterol.