Large-scale retrospective analyses of the effect of iron deficiency anemia on hemoglobin A1c concentrations

•Patients with iron deficiency anemia can have increased hemoglobin A1c levels.•Both females and males, HbA1c levels significantly decreased as serum iron and iron saturation increased.•No significant correlation between TIBC and HbA1c was observed for female patients.•Clinicians should consider IDA status before making any therapeutic decisions when monitoring A1c levels. HbA1c is a reliable biomarker for diagnosing and prognosis of diabetes, but many clinical scenarios and interfering factors can affect the test results. Any conditions that affect red cell turnover, such as iron-deficiency anemia (IDA), can lead to spurious HbA1c results. Reports on how IDA affects HbA1c concentrations are contradictory, and to understand better the association between HbA1c concentrations and IDA, we conducted a large-scale retrospective study. Test results for HbA1c concentrations were retrieved from the years 2015–2019. We evaluated over 12,000 patients with IDA and 21,000 patients without IDA. Patients were classified as having IDA if samples with below the age-based ranges for serum iron, ferritin, or transferrin iron saturation and above age-based ranges for transferrin iron-binding capacity or transferrin concentrations. Kruskal–Wallis statistical analyses method was used to test whether the two samples follow the same distribution and significance. The median HbA1c concentration was 5.7% among IDA classified patients and 5.4% among normal samples (P