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By the way, doctor: Can you help me make sense of these diabetes tests?

By the way, doctor

Can you help me make sense of these diabetes tests?

Q. What does it mean if my fasting blood sugar level is high (135–145) but my glycosylated hemoglobin test is negative?

A. The American Diabetes Association (ADA) defines diabetes as having a fasting blood sugar level of 126 mg/dL or higher on at least two occasions. Hemoglobin is the molecule in red blood cells that serves mainly as an escort for oxygen. But it also combines with sugar, or glycosylates. Measuring the percentage of hemoglobin that’s glycosylated is a good way to assess whether you’ve had high blood sugar over the past several months. The blood sugar test is more of a snapshot.

The ADA doesn’t recommend using glycosylated hemoglobin levels for diagnosis, partly because the definition of normal varies from lab to lab. But in reality, I and many other doctors order the test, often referred to by the initials HbA1c. It helps us distinguish a borderline case from a full-blown one.

It’s questionable whether patients like you — with moderately elevated blood sugar levels but normal glycosylated hemoglobin — should be classified as having diabetes. You should get a second fasting blood test. But even if that test comes back high, the fact that your glycosylated hemoglobin level is normal (defined as 6% or less) is an indication that your diabetes is mild.

Some doctors prescribe metformin (Glucophage) because it can keep mild diabetes from getting worse. But several years ago, a large study showed that lifestyle changes are actually better at delaying diabetes. Those changes include eating a low-calorie diet; exercising regularly (half an hour daily of brisk walking or other moderately intense activity); and losing weight (a 5%–7% reduction). Doing all that isn’t easy, but I think it’s important to try before starting medication.

You should have your blood sugar and glycosylated hemoglobin levels checked regularly. Diabetes is a major risk factor for heart disease as well as for eye, kidney, and neurological problems. You and your doctors can work to offset these risks by monitoring your blood pressure (don’t let it get above 130/80) and LDL cholesterol (keep it under 100). And talk to your doctor about taking an 81-mg “baby” aspirin for protection against heart disease and stroke. When patients of mine are newly diagnosed with diabetes, I also examine them for any signs of nerve damage and refer them to a specialist for an eye exam.

— Nancy Keating, M.D. Brigham and Women’s Hospital Harvard Health Letter Editorial Board

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Last updated:	August 21, 2006