Evaluation of Preanalytical Variables and the Use of Alternative Anticoagulants in HbA1c Testing

Abstract

Introduction: Preanalytical variables significantly influence laboratory testing accuracy, and their impact on glycated haemoglobin (HbA1c) measurements remains a critical area of study. HbA1c is widely used for diagnosing and monitoring diabetes mellitus, with EDTA being the standard anticoagulant. However, challenges such as sample underfilling and alternative anticoagulant use remain underexplored.

Objectives: This study examines the effects of preanalytical factors, including underfilled sample volumes and alternative anticoagulants, on HbA1c reliability.

Methods: We analysed 150 blood samples collected from adult patients. Samples were collected in tubes containing K3-EDTA, K2-EDTA, and lithium heparin at varying fill volumes. HbA1c concentrations were measured using a standardized immunoturbidimetric assay on the Cobas c 6000 platform. Results were analysed using paired t-tests, Wilcoxon signed-rank tests, and bias analysis. The clinical impact was assessed against the diagnostic cutoff of HbA1c ≥6.5%.

Results: Underfilled EDTA tubes (<50%) showed statistically significant deviations in HbA1c measurements (P < 0.05), with greater bias observed below the diagnostic threshold of 6.5%. Lithium heparin demonstrated acceptable stability compared to K3-EDTA but introduced variability at higher HbA1c levels. Bias analysis indicated minimal clinical relevance when anticoagulants were used appropriately, but underfilled samples produced erroneous classifications in up to 10% of cases.

Conclusions: Preanalytical variables, particularly fill volume, must be tightly controlled in HbA1c testing to ensure diagnostic reliability. While alternative anticoagulants like lithium heparin may provide flexibility, their adoption requires thorough validation under specific conditions. Laboratories should implement strict quality control protocols to mitigate preanalytical errors.