HbA1c results may be affected by anemia

Anemia affects the reliability of HbA1c results, concluded a new systematic review that offered 4 tips for incorporating this knowledge into clinical practice.

Reviewers identified 12 studies published between January 1990 and May 2014 that all had at least 1 measurement of HbA1c and glucose and a least 1 index of hematinic deficiency in nonpregnant adults who were not known to have diabetes. Results were published by Diabetologia on May 21.

Eleven of the 12 studies focused on iron deficiency anemia, and together they showed that anemia can have a significant impact on HbA1c values, since a “spuriously high” HbA1c is present in iron deficiency anemia compared with other markers of glycemia. “Together, these data support the hypothesis that iron deficiency per se may cause elevated HbA1c values, irrespective of anemia,” the authors wrote.

They continued, “If the estimated upward shift in HbA1c values seen with iron deficiency is combined with the apparent increased prevalence of prediabetes, it may result in a significant number of patients where the combination of the two will be sufficient to shift HbA1c values to move from a diagnosis of prediabetes to diabetes.”

The researchers found less data on non-iron deficiency forms of anemia, but those available indicated that that these conditions may decrease HbA1c values.

For clinical practice, this means 4 things, the authors wrote:

1. 1. When monitoring people with diabetes, consider abnormalities of erythrocyte indices when glucose and HbA1c are discordant.
2. 2. When HbA1c is normal or elevated but hemoglobin is low, do not assume that HbA1c is falsely elevated. Check erythrocyte indices, in particular, mean corpuscular volume and mean corpuscular hemoglobin. If they are if low, consider iron deficiency by transferrin saturation or ferritin. If mean corpuscular volume and mean corpuscular hemoglobin are not low, then consider other forms of anemia. (The authors added that ferritin as a marker of iron status is useful if it is low, but it does not rule out iron deficiency if it is normal or elevated, because inflammation may mask a low ferritin level.)
3. 3. Iron deficiency, as well as iron deficiency anemia, may be enough to change HbA1c values, especially in women of childbearing age.
4. 4. If abnormalities of erythrocyte indices or anemia are found, consider correction of the abnormality before using HbA1c for diagnosis or monitoring. It may take up to 6 months after treatment is started to normalize erythrocyte indices. Red cell distribution width can provide an additional indicator of normalization of the erythrocyte population and erythrocyte lifespan.