Exams and Tests

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

If the patient is having symptoms but are not known to have diabetes, evaluation should always begin with a thorough medical interview and physical examination. The healthcare provider will about symptoms, risk factors for diabetes, past medical problems, current medications, allergies to medications, family history of diabetes or other medical problems such as high cholesterol or heart disease, and personal habits and lifestyle.

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

Finger stick blood glucose: This is a rapid screening test that may be performed anywhere, including community-based screening programs.

• A fingerstick blood glucose test is not as accurate as testing the patient's blood in the laboratory but is easy to perform, and the result is available right away.
  
  
• The test involves sticking the patient's 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 true 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 people with diabetes monitor their blood sugar levels at home.

Fasting plasma glucose: The patient will be asked to eat or drink nothing for 8 hours before having 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, they 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 the patient may undergo an oral glucose tolerance test or a glycosylated hemoglobin test (often called "hemoglobin A1c") as a confirmatory test.
  
  
• If fasting plasma glucose level is greater than 100 but less than 126 mg/dL, then the patient has what is called impaired fasting glucose, or IFG. This is considered to be pre-diabetes. The patient does not have diabetes, but they 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, then drawing blood for a second test at two hours after drinking 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, the patient has diabetes.
  
  
• If the blood glucose level is between 140 and 199, then the patient has impaired glucose tolerance (IGT), which is also a pre-diabetic condition.

Glycosylated hemoglobin or hemoglobin A1c: This test is a measurement of how high blood sugar levels have been over about the last 120 days (the average life-span of the red blood cells on which the test is based).

• Excess blood glucose hooks on to the hemoglobin in red blood cells and stays there for the life of the red blood cell.
  
  
• 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 indicates good glucose control. A result of 8% or greater indicates that blood sugar levels are too high for too much of the time.
  
  
• The hemoglobin A1c test is less reliable to diagnose diabetes than for follow-up care. Still, 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 three to six 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 laboratory to laboratory, although an effort is under way to standardize how measurements are performed.

Diagnosing complications of diabetes

If you or someone you know has diabetes, the patient should be checked regularly for early signs of diabetic complications. The healthcare provider can do some of these checks; for others, the patient should be referred to a specialist.

• The patient should have their eyes checked at least once a year by an eye specialist (ophthalmologist) to screen for diabetic retinopathy, a leading cause of blindness.
  
  
• The patient's urine should be checked for protein (microalbumin) on a regular basis, at least one to two times per year. Protein in the urine is an early sign of diabetic nephropathy, a leading cause of kidney failure.
  
  
• Sensation in the 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.
  
  
• The healthcare provider should check the feet and lower legs at every visit for cuts, scrapes, blisters, or other lesions that could become infected.
  
  
• The patient should be screened regularly for conditions that may contribute to heart disease, such as high blood pressure and high cholesterol.

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