Comparison of longitudinal point-of-care and high-performance liquid chromatography HbA1c measurements in a multi-centre trial

Aims Point-of-care HbA1c is routine in clinical practice. Comparison of point-of-care HbA1c against laboratory measurements across sites and over time is warranted. Methods One hundred and twenty-one young persons with Type 1 diabetes from four centres provided 450 paired samples collected over 10 months for point-of-care HbA1c and central laboratory-based high-performance liquid chromatography (HPLC) HbA1c determinations. Change in HbA1c over time was assessed by difference from initial to final HbA1c and by growth modelling with annualized slope calculation. Change in HbA1c was categorized as improved (decrease of = 0.5% or negative slope), no change (+/- 0.4% of initial HbA1c or slope = 0) or worsened (increase of = 0.5% or positive slope). Results The 450 paired samples (median of four pairs/patient) were highly correlated (r = 0.97, P < 0.0001), as were time-specific and site-specific pairs (r = 0.94 to 0.98, P < 0.0001). Initial-to-final point-of-care HbA1c and HPLC HbA1c changes were 0.3 +/- 1.1% (range -2.7 to 4.1) and 0.4 +/- 1.2% (-3.9 to 4.5), respectively, with 21% of patients (n = 26) discordant for change categories. ?HbA1c by point-of-care HbA1c vs. HPLC HbA1c differed across the HbA1c range and by = 0.5% absolute difference in ?HbA1c in 14 (54%) of the 26 patients discordant for HbA1c change categories. Mean annual HbA1c slope was 0.4 +/- 1.5% (-5.4 to 4.8) for point-of-care HbA1c and 0.4 +/- 1.6% (-6.9 to 5.2) for HPLC HbA1c, with 18% (n = 22 pairs) discordant for change categories. Conclusions Assessment of absolute HbA1c change may not be different for point-of-care HbA1c compared with HPLC HbA1c; however, misclassification of patients by discrete cut-off values may occur with point-of-care HbA1c compared with HPLC HbA1c determinations.