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A1c (HbA1c, Hemoglobin A1c, Glycated Hemoglobin) is the gold standard for control of diabetes. It measures the percent of glycation of the oxygen carrying proteinA1c (hemoglobin) in the red blood cell. Red blood cells are constantly being made and destroyed. As a red blood cell is made, it takes up glucose (sugar) in an amount based on the blood glucose level at the time (glycation). Since this is a relatively stable process for the life of the red blood cell, a measure of the percent of glycation gives an estimate of the average blood glucose (sugar) for the average life of red blood cells (about 8 -12 weeks). The small blue balls in the image represent blood glucose(sugar) and the large red ball a red blood cell. When blood sugar is relatively low, there will be less glucose attached to the cell, when high more is attached.


The American Diabetes Association recommends a target A1c less than 7% and the American Association of Clinical Endocrinologists less than 6.5%. Each emphasizes the need to individualize targets for patients. What’s a good target for one may be dangerous for another. All people with diabetes should consult their physician and/or diabetes team for an individualized target. a1c_chart

It is important to remember that there are some factors that will produce an erroneous A1c. Conditions that increase red blood cell turnover (breakage of cells, blood loss) recent transfusions, treated vitamin B12 or folate deficiency anemias, hemoglobin variants such as Sickle Cell or other inherited processes all may cause a falsely low value. Conversely, low turnover states, e.g. untreated vitamin deficiency anemias, may result in false high values.

A1c measurements may vary, a blood sample sent to one lab may vary as much as 10% at another. So an A1c of 7.5% at one lab may be reported as 8.3% at another.

A1c provides a snapshot of an approximate average blood glucose (sugar) for the previous three months. It does not give any information about highs and lows. We have seen cases where the patient was having wide swings in blood glucose (sugar), sometimes very high and sometimes very low but with an A1c at 6.4%. Ordinarily we would be happy with A1c of 6.4% but in this case it is obvious that adjustments are needed.

The chart to the left is based on:Defining the Relationship Between Plasma Glucose and HbA1c: DIABETES CARE, VOLUME 25, NUMBER 2, FEBRUARY 2002. Click here to see article.

Updated: September 16, 2013

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