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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+1.00 x ( 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. [ABSTRACT FROM AUTHOR]