Anaemia can lead to a false diagnosis of diabetes based on HbA1c, according to a review published in Diabetologia. 

The analysis of 12 studies found that in general, the presence of iron deficiency with or without anaemia led to an increase in HbA1c values compared with controls, with no corresponding rise in blood glucose.

“This may lead to confusion when diagnosing diabetes using HbA1c,” said the authors led by Dr Emma English, University of Nottingham, UK.

There was currently insufficient data to fully inform clinicians and scientists on how to address this in clinical practice. However, while clarity is awaited the authors suggest:

1. During monitoring of people with diabetes, when glucose and HbA1c are discordant, consider abnormalities of erythrocyte indices.

2. When HbA1c is normal/elevated but Hb is low, do not assume that HbA1c is falsely elevated—check erythrocyte indices, in particular MCV and MCH; if low, consider iron deficiency by TSAT or ferritin. If MCV and MCH are not low then consider other forms of anaemia—HbA1c may be falsely decreased in these cases.

3. Iron deficiency, as well as IDA, may be sufficient to cause a change in HbA1c values; this is highly relevant in wom- en of childbearing age.

4. If abnormalities of erythrocyte indices or anaemia are identified, consider correction of the abnormality before using HbA1c for diagnosis or monitoring. The studies included in this review suggest that it may take up to 6 months after treatment is initiated to normalise erythrocyte indices. RDW will provide an additional indicator of normalisation of the erythrocyte population and erythrocyte lifespan.

“The key questions that are still to be answered are whether anaemia and erythrocyte abnormalities will have a significant impact on the diagnosis of diabetes using HbA1c in the general population—something that is now widely performed,”they conclude.