Our objective was to compare in a prospective study the clinical performance of the reference and an alternative method to measure blood levels of glycated hemoglobin. A total of 178 samples from patients with diabetes were tested by both methods, and results were analyzed for correlation and comparison of sensitivity, specificity, and positive and negative predictive values to classify patients according to glycemic control. There was a significant linear correlation between methods (r = 0.645; P < .0001); the sensitivity, specificity, and positive and negative predictive values of the alternative method to identify patients with controlled and uncontrolled status were as follows: controlled, 88%, 78%, 77%, and 88%; and uncontrolled, 78%, 88%, 88%, and 77%, respectively. Results show that although the results of both methods show a statistically significant correlation, the ability of the alternative method to correctly classify individual patients according to glycemic control status is far from optimal.