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Diabetes (Mellitus, Type 1 and Type 2) (cont.)

Diabetes Diagnosis

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

The health care professional will take a history including information about the patient's 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.

  • Although a not as accurate as testing the patient's blood in the hospital laboratory, a fingerstick blood glucose test 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% to 20% of true laboratory values.
  • Fingerstick blood glucose values tend to be most inaccurate at very high or very low levels, so this test is only a preliminary screening study. Fingerstick 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 prediabetes. These patients do 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 up to 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 prediabetic condition.

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

  • Excess blood glucose hooks itself 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, too much of the time.
  • The hemoglobin A1c test is the best test for diabetes follow-up care, than to diagnose diabetes. 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 3 to 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 laboratory to laboratory, although an effort is under way to standardize how measurements are performed.
Medically Reviewed by a Doctor on 4/3/2014

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