Background: Conditions that affect erythrocyte turnover affect HbA1c concentrations. Although many forms of anemia are associated with lowering of HbA1c, iron deficiency tends to increase HbA1c. We examined the effect of iron and hemoglobin (Hb) status on HbA1c and on the relationship between concentrations of fasting glucose and HbA1c in a national sample of adults in the US.
Methods: Cross-sectional data from 8296 adults aged ≥20 years who participated in NHANES 1999–2002 were used.
Results: The prevalence of low Hb (defined as <120 and <118 g/L in women aged 20–69 and ≥70 years, respectively, and <137, <133, and <124 g/L in men aged 20–49, 50–69, and ≥70 years, respectively) was 5.5%. There was a significant positive correlation between Hb concentrations and HbA1c concentrations after adjusting for age, gender, and race or ethnicity, with HbA1c rising from a mean of 5.28% among participants with Hb <100 g/L to 5.72% among participants with Hb ≥170 g/L. The adjusted mean concentrations of HbA1c were 5.56% and 5.46% among participants with and without iron deficiency, respectively (P = 0.095). However, there was no evidence of differences in the relationship between fasting glucose and HbA1c when groups of anemic and non-anemic individuals with and without iron deficiency were examined individually.
Conclusions: Caution should be used when diagnosing diabetes and prediabetes among people with high or low Hb when the HbA1c level is near 6.5% or 5.7%, respectively, as changes in erythrocyte turnover may alter the test result. However, the trend for HbA1c to increase with iron deficiency does not appear to require screening for iron deficiency in ascertaining the reliability of HbA1c in the diagnosis of diabetes and prediabetes in a given individual.