Friday, July 20, 2007

A Change May Be In the Works for HbA1c

You've just had an A1C (hemoglobin A1C) test. The result was 7.5%. What does that mean? How does that relate to the average blood glucose readings you take at home? If preliminary results from the ADAGE trial hold, that A1C lab result may be reported as average glucose, in the familiar mg/dl reading, beginning next year.

The ADAGE study is a clinical trial being conducted at a number of centers across North America, Europe, and Africa. Its goal is to confirm the relationship between HbA1C levels and average blood glucose. Preliminary findings, reported at the 2007 ADA Scientific Sessions, are showing that relationship is closely correlated, for both type 1 and type 2 diabetes. This could lead to results of an A1C test being reported as A1C-Derived Average Glucose (ADA-G).

What Is HbA1C?

Hemoglobin A1C is that portion or percent of total hemoglobin that has glucose attached to it. In people without diabetes, about 4% to 6% of their hemoglobin is glycosylated. Red blood cells that contain the hemoglobin circulate in the bloodstream for 3 or 4 months before being broken down and replaced. During that time the RBC can bond, irreversibly, to glucose in the bloodstream. Thus, A1C readings higher than about 6% indicate higher than normal amounts of glucose roaming the bloodstream in the past 120 days.

Using the Conversion Table from the ADA's 2005 Position Statement on Standards of Medical Care in Diabetes, the 7.5% A1C reading at the beginning of this post would equate to an average blood glucose of about 188 mg/dl:

If this change happens, instead of receiving a 7.5% HbA1C, you might receive a result such as 188 mg/dl ADA-G. Improved calibration of lab machines that measure glycosylated hemoglobin are also in the offing. These changes may make lab results easier to interpret leading to improved blood glucose management.