Standardization of HbA1c Assays: Impact of IFCC Reference Method on Diabetes Diagnosis

Abstract

Introduction: Hemoglobin A1c (HbA1c) is the gold standard for glycemic monitoring and diabetes diagnosis. The IFCC reference method has improved standardization, but method-related variability and hemoglobinopathy interference remain challenges.
Methods: Systematic review of 22 studies (n=15,673) comparing IFCC-standardized HbA1c (NGSP-certified) versus non-standardized assays. Reference: IFCC primary reference measurement procedure. Outcomes: between-laboratory coefficient of variation (CV), misclassification of diabetes (HbA1c ≥6.5%), correlation with mean glucose.
Results: IFCC-standardized assays reduced between-laboratory CV from 5.2% to 2.1% (p<0.001). Misclassification rate fell from 8.7% to 2.4% (p=0.002). However, 12% of laboratories still used unstandardized methods in low-resource settings. Hemoglobinopathies (HbS, HbC, HbE) caused falsely low HbA1c in 4.2% of samples using immunoassays, but not with HPLC or capillary electrophoresis.
Discussion: Standardization dramatically improved accuracy, but global adoption is incomplete. Hemoglobin variants require alternative methods or fructosamine.
Conclusion: IFCC-standardized HbA1c assays are essential for reliable diabetes diagnosis. Laboratories must use HPLC/electrophoresis to detect variant interference.