Fluoride-Oxalate and Lithium Heparin Anticoagulant Tubes Are Reliable Alternatives to EDTA for HbA1c Measurement.

BACKGROUND: The dual role of HbA1c in diagnosing and monitoring diabetes mellitus has driven a continuous increase in routine testing requests. To optimize laboratory workflows and avoid dedicated EDTA blood draws, this study is aimed at determining whether fluoride-oxalate and lithium heparin anticoagulant tubes could serve as reliable alternatives to EDTA tubes for HbA1c measurement on the COBAS INTEGRA 400 plus analyzer. METHODS: Over 2 months at the Pasteur Institute of Tunis, paired blood samples from patients undergoing routine HbA1c testing were analyzed. Standard K3-EDTA tubes were compared with either lithium heparin or fluoride-oxalate tubes using a turbidimetric inhibition immunoassay on a COBAS INTEGRA 400 plus analyzer. The study relied exclusively on residual clinical material without imposing specific preanalytical restrictions. RESULTS: The study population comprised 277 patients, divided into Group 1 (K3-EDTA vs. fluoride-oxalate, n = 200) and Group 2 (K3-EDTA vs. lithium heparin, n = 77). HbA1c results from both alternative tubes showed strong correlation with K3-EDTA (r = 0.99, p < 0.0001), with no significant overall differences. Passing-Bablok regression revealed no constant or proportional bias for lithium heparin, whereas a systematic bias was observed for fluoride-oxalate. Bland-Altman analysis of log-transformed data indicated no significant mean bias for either fluoride-oxalate (-0.15%; 95% LoA [-2.76% to +2.53%]) or lithium heparin (-0.04%; 95% LoA [-2.77% to +2.76%]), although a slight proportional bias was detected in both. Finally, HbA1c measurements in both tube types exhibited high diagnostic performance at clinical cutoffs (p < 0.0001). CONCLUSIONS: Fluoride-oxalate and lithium heparin anticoagulant tubes provide reliable alternatives to standard K3-EDTA tubes for HbA1c measurement, with no clinically meaningful differences observed. However, we emphasize that these results are strictly validated for the Roche COBAS immunoassay.