Can Hemoglobin A1c go too low?

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A new study showing increased mortality among type 2 diabetes patients at hemoglobin A1c levels below 7.5% raises a new question: Should diabetes guidelines be revised to include a minimum hemoglobin A1c level?

In the study of nearly 48,000 patients, published in the January 27th issue of the Lancet, the 10% of patients with the lowest hemoglobin A1c values (less than 6.7%) had higher death rates than all but the those in the top 10% (9.9% or higher). Those in the middle, with an average A1c of 7.5%, had the lowest death rate.

Lead author Dr. Craig Currie, of Cardiff University, Wales, and his associates concluded that “if confirmed, diabetes guidelines might need revision to include a minimum A1c value.” And in an accompanying editorial, Drs. Beverley Balkau and Dominique Simon of the CESP Centre for Research in Epidemiology and Population Health, Villejuif, France, said the study “does provide a rationale for an HbA1c threshold of 7.5% corresponding to the lowest death rate and lowest event rate for large-vessel disease.”

Currently, the American Diabetes Association recommends a target hemoglobin A1c of less than 7.0%, while the American Association of Clinical Endocrinologists’ recommendation is 6.5% or less. However, both organizations advise that the goals be individualized based on patient factors such as comorbid conditions, history of hypoglycemia, education, and life expectancy.

Clearly, the thinking has shifted since the 1990’s when both the Diabetes Control and Complications Trial and the United Kingdom Prospective Diabetes Study led many to conclude-with the focus on microvascular complications-that there was no lower threshold for risk reduction as long as severe hypoglycemia was avoided.

But then in 2008 came the startling results from the ACCORD trial in which mortality was significantly increased among patients randomized to more intensive glucose-lowering therapy (although those with A1c levels below 7% in the intensive arm had lower mortality than did those with higher A1cs). Experts are still debating the implications of those findings, in the face of other conflicting data. Among the unanswered questions: Is hypoglycemia itself a cardiovascular risk factor?

Obviously more data are needed. Until then, the only thing certain is that there’s more debate to come.

-Miriam E. Tucker  (@MiriamETucker on Twitter)

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3 Comments

Filed under Cardiovascular Medicine, Endocrinology, Diabetes, and Metabolism, Family Medicine, Geriatric Medicine, IMNG, Internal Medicine, Primary care

3 responses to “Can Hemoglobin A1c go too low?

  1. Pingback: Can an A1C be too low?

  2. Pingback: The Top-Viewed Posts of 2010 | EGMN: Notes from the Road

  3. Jerrymat

    Dr. Richard Bernstein, in his book on diabetes, teaches that every diabetic should aspire to normal blood sugars. His book tells how to achieve that. I wonder, if the statistics regarding A1c are really mixing two kinds of diabetic patients: those who allow their blood sugars to go quite high and try to compensate with too much insulin (leading to hypoglycemia) and those who follow Dr. Bernstein, modify their diet severely, so that they need the smallest doses of insulin. My doctor is having fits because I have lowered my A1c to 5.1.

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