Factors affecting A1C in non-diabetic individuals: Review and meta-analysis.

We carried out a systematic review and meta-analyses of studies that evaluated the possible effects of anemia, variant hemoglobin, and uremia on A1C levels in individuals without diabetes (DM). Medline and Embase were searched for studies that measured A1C values in groups with and without iron deficiency anemia (IDA) and/or iron deficiency (ID), variant hemoglobin and/or uremia by standardized methods. The difference between A1C levels in the groups with and without interferences was obtained by using random-effects meta-analysis and the effect size was presented as absolute difference of means (95% CI). Ten studies fulfilled the inclusion criteria, providing data from 11,176 participants without DM. There were no statistically significant differences in A1C in the presence of IDA/ID, HbS, and uremia by HPLC and uremia by immunoassay [0.79% (95% IC -0.39; 1.97), -0.13% (95% IC -0.51; 0.26), 0.15% (95% CI -0.58; 0.88) and -0.19% (95% CI -0.78; 0.40), respectively]. The effects of HbAS and uremia on A1C levels are within the expected individual variation and should not affect A1C results to diagnose DM. However, the effects of IDA/ID remain inconclusive and further studies are needed to clarify the glycation mechanisms in individuals with IDA/ID without diabetes.