Diabetes Monitor - Information, education, and support for people with diabetes

Why Not Use The A1c To Diagnose Diabetes?

Publication Date: 11/17/2004

Remember that the information presented here is not intended to replace the care of your own doctor. Before making any changes in the management of your own illness, you should consult your physician or other qualified medical professionals.


 

Question

The screening for diabetes is simple, quick, and not expensive, but it is not a diagnosis. I assume that this screening is on the basis of a random plasma glucose test (just a regular fingerstick) — am I right? How valuable do you think screenings like this are? I'm sure that the other accepted diagnostic tests (e.g., a plasma glucose value of 126 mg/dl [7 mm/l] or more after an 8-hour fast or an oral glucose tolerance test) are impractical for mass screening, but I don't understand why the A1c is not an acceptable diagnostic tool. Is it acceptable if the level is high enough?

Answer

Traditionally, diabetes is diagnosed by elevated blood sugar values. Symptoms are optional, because sometimes people have symptoms mimicking diabetes, but in fact the symptoms are later found to be due to other causes. Urine sugars would be misleading since they might be falsely positive in the rare syndrome of renal glycosuria and falsely negative if someone has a high renal threshold or mildly elevated blood sugars.

Why not use HbA1c? Not because the ADA makes the pronouncement that

The use of the hemoglobin A1c (A1C) for the diagnosis of diabetes is not recommended at this time. (See DIAGNOSTIC CRITERIA FOR DIABETES MELLITUS, and notice they don't give a reference for their statement!)

I think it's simply since no one has done the clinical trials needed to ascertain the utility of the A1c in diagnosing diabetes. Additionally, older A1c methods could be confounded by abnormal hemoglobins, which would give elevated results in A1c assays even in people without diabetes.

I usually ordered both blood glucose and A1c if a patient presented with symptoms of diabetes. If both are elevated, it helps nail the diagnosis, and gives a baseline A1c for later comparison.

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