A1C affected by

Hemoglobin A1c (HbA1c) is a widely used laboratory assay for glycated hemoglobin and is reported as a percentage of glycated hemoglobin in the sample.  The rate of glycation is proportional to the ambient glucose concentration.  Because hemoglobin levels are usually stable, HbA1c can be used as a marker for glycemic control in patients with diabetes mellitus and reflects mean plasma glucose over 8-12 weeks.

However, HbA1c is vulnerable to changes in hemoglobin production and survival.  Patients with conditions that cause reduced red blood cell survival (eg, hemolytic anemia) have a greater proportion of new red blood cells (ie, with nonglycated hemoglobin) and therefore a misleadingly low HbA1c.  Conversely, those with reduced blood red cell production (eg, due to iron deficiency, as in this patient) have a lower proportion of new red cells and a misleadingly high HbA1c.

In such cases, the underlying hematologic condition should be corrected and the HbA1c rechecked.  Alternately, serum fructosamine, which measures glycation of serum proteins, can be ordered; this test estimates glycemic control over 2-3 weeks.

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