Toward standardized antithrombin activity assays: multi-center evaluation and optimization

Antithrombin (AT) is a critical anticoagulant whose deficiency, which is common in many clinical conditions, requires precise management. The multi-center evaluation revealed significant bias and poor reproducibility at AT activity levels below 30%, and some even fail to provide reliable results. In this study, the assay performance for Systems A and B was substantially improved through tailored optimization strategies involving standardized reagent reconstitution, the establishment of low-level calibration curves, and the implementation of low-level quality control. Following optimization, bias at the 15% level was markedly reduced, coefficients of variation were improved, and reproducibility was significantly enhanced. Compared with the measurements before optimization, the low-level material results were closer to the target levels, and the recovery rates were improved. Importantly, the standardized workflow and optimization measures proposed in this study can be translated into a practical laboratory operating guide to support personnel training across laboratories and lay a solid foundation for forming professional guidelines or expert consensuses in the future.