Assessment of the Performance of A1CNow ⁺ and Development of an Error Grid Analysis Graph for Comparative Hemoglobin A1c Measurements

BACKGROUND: This study investigated the performance of the A1CNow(+®) test (Bayer Diabetes Care, Sunnyvale, CA) in a large population of Chinese patients with diabetes. SUBJECTS AND METHODS: Hemoglobin A1c (HbA1c) levels in 1,618 Chinese patients with diabetes 10-94 years of age were measured with both the A1CNow(+) test, from a fingerstick blood sample, and the high-performance liquid chromatography (HPLC) test, using a venous blood sample, within 24 h. The reportable ranges of the HbA1c values were 4.0-13.0% (A1CNow(+)) and 4.1-16.8% (HPLC). An error grid analysis (EGA) method was developed to quantify the accuracy of the A1CNow(+) results against the HPLC reference results. RESULTS: The A1CNow(+) results were highly correlated with the HPLC reference results (r=0.945, P<0.01). Passing-Bablok regression analysis showed a good linear agreement between the two variables, and the linear regression equation fitted as y=-0.10+1.00x (P=0.21). The Bland-Altman difference plot presented that the mean bias of the A1CNow(+) results minus the HPLC reference results was -0.09% (P<0.001); the 95% confidence intervals for the limits of agreement were -1.28% to 1.09%, with 96.5% of the data points lying within this zone. The results of the EGA showed that 80.2% of the A1CNow(+) results were accurate, 17.7% were acceptable, 1.9% may lead to inappropriate treatment, and 0.3% may lead to severe clinical consequence. CONCLUSIONS: The A1CNow(+) test values demonstrated a slight negative bias from the HPLC values. The majority of A1CNow(+) test values were accurate when compared with results from the reference method.