Agreement between HbA1c measured by DCA 2000 and by HPLC: Effects of fetal hemoglobin concentrations

Background jects with type 1 diabetes, persisting elevations of fetal hemoglobin (HbF) have been demonstrated. This study evaluated whether HbF levels typically seen in type 1 diabetes (up to 3%) interfere with glycohemoglobin determinations using a common immunologic method (DCA 2000™). s was measured by high-performance liquid chromatography (HPLC) using a Diamat™ analyzer in 90 type 1 diabetics with parallel determinations of HbF. Results were compared with HbA1c concentrations obtained using DCA 2000™. s ucibility was good for both methods with coefficients of variation <5% and correlation between the two methods was good (r2 = 0.939, p<0.0001). Mean difference between the two methods was small (0.007%). Limits of agreement varied between −0.92% and +0.93% (95% confidence interval [95% CI]) and constant bias (intercept: 0.73 95% CI 0.28–1.18) as well as a proportional bias (slope: 0.92 95% CI 0.87–0.97) were detected. At low concentrations of HbF, the DCA 2000™ immunologic method tended to underestimate and at higher concentrations tended to overestimate HbA1c when compared with Diamat™. Stepwise linear regression with HbA1c (DCA 2000™) as dependent variable included HbA1c (Diamat™) and HbF in the model (r2 = 0.946, p<0.0001), explaining 94.6% of the variability of HbA1c (DCA 2000™). Partial correlation coefficient between HbA1c (DCA 2000™) and HbF corrected for HbA1c (Diamat™) was 0.337 (p = 0.0012). sions 00™ allowed measurements of HbA1c rapidly and with precision adequate for clinical purposes. However, agreement with Diamat™ results was comparatively weak with both constant as well as proportional biases. The 95% limits of agreement between Diamat™ and DCA 2000™ fell within a range that significantly limited traceability between these two methods; therefore, the two methods should not be used interchangeably. Small but persistent elevations of HbF concentrations were identified as a significant cofactor, which may be relevant for limited traceability between the two methods.