Analytic Bias Among Certified Methods for the Measurement of Hemoglobin A1c : A Cause for Concern?

• Published in: American journal of clinical pathology Vol. 129; no. 4; pp. 540 - 547
• Main Authors: HOLMES, Earle W, ERSAHIN, Cagatay, AUGUSTINE, Geri J, CHARNOGURSKY, Gerald. A, GRYZBAC, Margie, MURRELL, Joanne V, MCKENNA, Kathleen M, NABHAN, Fadi, KAHN, Stephen E
• Format: Journal Article
• Language: English
• Published: Chicago, IL American Society of Clinical Pathologists 01.04.2008
• Subjects: Bias; Biological and medical sciences; Blood Chemical Analysis - standards; Blood Chemical Analysis - statistics & numerical data; Glycated Hemoglobin A - analysis; Humans; Investigative techniques, diagnostic techniques (general aspects); Laboratories - standards; Medical sciences; Pathology. Cytology. Biochemistry. Spectrometry. Miscellaneous investigative techniques; Point-of-Care Systems; Predictive Value of Tests; Quality Control; Reproducibility of Results; Analytic error; Hemoglobin A; Point-of-care testing; Anatomic pathology; Hemoglobin A1c; Bias; Method; Diabetes; Quantitative analysis
• ISSN: 0002-9173; 1943-7722
• DOI: 10.1309/U3GPPTCBP1VLL8AW

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.