title: Analytic bias among certified methods for the measurement of hemoglobin A1c: a cause for concern?
abstract: We studied the magnitude, significance, and origin of an analytic bias that emerged between our point-of-care (POC) and our central laboratory (CL) methods for the measurement of hemoglobin A1c (HbA1c) and evaluated the analytic accuracy of 7 commonly used HbA1c methods relative to the National Glycohemoglobin Standardization Program (NGSP) reference method. The POC and CL methods were compared by split-sample analysis of clinical specimens and time series analyses of the HbA1c results reported for a 33-month period. The relative accuracies of 7 HbA1c methods were evaluated using College of American Pathologists proficiency survey results. Long-term drifts in the CL- and POC-analyzed test results caused the median intermethod bias [(POC result)-(CL result)] to increase from -0.4% to -0.9% HbA1c. Systematic biases, drifts in analytic performance over time, and intermethod variability were frequently observed among the 7 NGSP-certified HbA1c methods. Intermethod variability is a potential source of inaccuracy whenever HbA1c results are interpreted relative to universal, fixed, clinical decision thresholds.
authors.affiliation: Department of Pathology, Loyola University Stritch School of Medicine, Maywood, IL 60153, USA.
authors.forename: Earle W
authors.initials: EW
authors.lastname: Holmes
authors.forename: Cağatay
authors.initials: C
authors.lastname: Erşahin
authors.forename: Geri J
authors.initials: GJ
authors.lastname: Augustine
authors.forename: Gerald A
authors.initials: GA
authors.lastname: Charnogursky
authors.forename: Margie
authors.initials: M
authors.lastname: Gryzbac
authors.forename: Joanne V
authors.initials: JV
authors.lastname: Murrell
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: McKenna
authors.forename: Fadi
authors.initials: F
authors.lastname: Nabhan
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Kahn
mesh_terms: D015982:Bias; D001774:Blood Chemical Analysis / Q000592:standards* / Q000706:statistics & numerical data; D006442:Glycated Hemoglobin / Q000032:analysis*; D006801:Humans; D007753:Laboratories / Q000592:standards*; D019095:Point-of-Care Systems; D011237:Predictive Value of Tests; D011786:Quality Control; D015203:Reproducibility of Results
chemical_list: D006442:Glycated Hemoglobin; C517652:hemoglobin A1c protein, human