BackgroundThis study aimed to investigate the relationship between HbA1c and RBC aggregation in type 2 diabetes mellitus (T2DM) patients by analysis of data from routine clinical tests and from in vitro experiments.MethodsA total of 2,111 inpatients with type 2 diabetes were selected and among them, 364 patients (Group A) had limited influence of plasma proteins on erythrocyte sedimentation rate (ESR) and was compared with the rest of the 1,747 inpatients (Group B). ESR, HbA1c, WBC, CRP, Fbg, and HCT were measured in all samples. Sixty samples were also collected from T2DM patients and used for in vitro ESR studies. Spearman's correlation coefficients were employed to reflect the correlation between ESR and other parameters. Mann–Whitney U test was used to compare the study parameters.ResultsThe test results for Group A were lower than Group B with respect to ESR, age, HCT, HbA1c, CRP, WBC, and Fbg. Only the difference in HbA1c, CRP, and Fbg values had statistical significance (P < 0.05). In addition, HbA1c correlated better with ESR for Group A (R = 0.622) than Group B (R = 0.563), whereas CRP and Fbg were contrary to this. In the in vitro studies, the HbA1c values were classified into the subgroups of 6.5–8.0%, 8.1–10%, and >10%. The corresponding ESR values were 28 ± 5.1 mm/h, 33 ± 2.7 mm/h, and 40 ± 4.1 mm/h, respectively.ConclusionESR results of T2DM patients were elevated that was mainly caused by Fbg levels, and in addition HbA1c in part contributed to RBC aggregation.