Comparison of longitudinal point-of-care and high-performance liquid chromatography HbA(1c) measurements in a multi-centre trial

Alleyn, C. R.; Laffel, L. M.; Volkening, L. K.; Anderson, B. J.; Nansel, T. R.; Wysocki, T.; Weissberg-Benchell, J.

Diabet Med. 2011 Aug 10; 28(12):1525-9

Abstract

Diabet. Med. 28, 1525-1529 (2011) ABSTRACT: Aims Point-of-care HbA(1c) is routine in clinical practice. Comparison of point-of-care HbA(1c) 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 HbA(1c) and central laboratory-based high-performance liquid chromatography (HPLC) HbA(1c) determinations. Change in HbA(1c) over time was assessed by difference from initial to final HbA(1c) and by growth modelling with annualized slope calculation. Change in HbA(1c) was categorized as improved (decrease of >/= 0.5% or negative slope), no change (+/- 0.4% of initial HbA(1c) 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 HbA(1c) and HPLC HbA(1c) 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. DeltaHbA(1c) by point-of-care HbA(1c) vs. HPLC HbA(1c) differed across the HbA(1c) range and by >/= 0.5% absolute difference in DeltaHbA(1c) in 14 (54%) of the 26 patients discordant for HbA(1c) change categories. Mean annual HbA(1c) slope was 0.4 +/- 1.5% (-5.4 to 4.8) for point-of-care HbA(1c) and 0.4 +/- 1.6% (-6.9 to 5.2) for HPLC HbA(1c) , with 18% (n = 22 pairs) discordant for change categories. Conclusions Assessment of absolute HbA(1c) change may not be different for point-of-care HbA(1c) compared with HPLC HbA(1c) ; however, misclassification of patients by discrete cut-off values may occur with point-of-care HbA(1c) compared with HPLC HbA(1c) determinations.

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