Liang Yideng, Jackson Joseph W, Woodle Samuel A, Surov Stepan S, Parunov Leonid A, Scott Dorothy E, Weinstein Mark, Lee Timothy K, Ovanesov Mikhail V
Center for Biologics Evaluation and Research U.S. Food and Drug Administration Silver Spring MD USA.
Res Pract Thromb Haemost. 2020 Dec 23;5(1):211-222. doi: 10.1002/rth2.12467. eCollection 2021 Jan.
Activated coagulation factor XIa (FXIa) is an impurity and primary source of procoagulant activity in thrombosis-implicated immune globulin (IG) products. Several assays, of varying quality and precision are used to assess FXIa-like procoagulant activity in units relevant to their respective principles.
To advance unified reporting, we sought to employ the World Health Organization reference reagents (RRs) to present the results of differing methodologies in units of FXIa activity and rank the sensitivity and robustness of these methodologies.
RR 11/236 served as a calibrator in several FXIa-sensitive blood coagulation tests: two commercial chromogenic FXIa assays (CAs); a nonactivated partial thromboplastin time (NaPTT); an in-house fibrin generation (FG) assay; an in-house thrombin generation (TG) assay; and an assay for FXIa- and kallikrein-like proteolytic activities based on cleavage of substrate SN13a. Some assays were tested in either normal or FXI-deficient plasma.
Each method demonstrated a sigmoidal dose-response to RRs. NaPTT was the least sensitive to FXIa and the least precise; our in-house TG was the most sensitive; and the two CAs were the most precise. All methods, except for SN13a, which is less specific for thrombotic impurities, gave comparable (within 20% difference) FXIa activity assignments for IG lots.
Purified FXIa reference standards support quantitation of FXIa levels in IG products in all tested assay methodologies. This should help to standardize the measurement of thrombotic potentials in IG products and prevent products exhibiting high procoagulant activity from distribution for patient use. Further research is needed to address the effect of IG product-specific matrixes on assay performance.
活化的凝血因子XIa（FXIa）是与血栓形成相关的免疫球蛋白（IG）产品中的一种杂质和促凝活性的主要来源。几种质量和精密度各不相同的检测方法被用于评估与其各自原理相关单位的FXIa样促凝活性。
为了推进统一报告，我们试图采用世界卫生组织参考试剂（RRs）以FXIa活性单位呈现不同方法的结果，并对这些方法的灵敏度和稳健性进行排名。
RR 11/236在几种FXIa敏感的血液凝固试验中用作校准物：两种商业显色FXIa检测法（CAs）；非活化部分凝血活酶时间（NaPTT）；一种内部纤维蛋白生成（FG）检测法；一种内部凝血酶生成（TG）检测法；以及一种基于底物SN13a裂解的FXIa和激肽释放酶样蛋白水解活性检测法。一些检测法在正常或FXI缺乏的血浆中进行了测试。
每种方法对RRs均呈现出S形剂量反应。NaPTT对FXIa最不敏感且最不精确；我们的内部TG最敏感；而两种CAs最精确。除对血栓杂质特异性较低的SN13a外，所有方法对IG批次的FXIa活性赋值相当（差异在20%以内）。
纯化的FXIa参考标准支持在所有测试的检测方法中对IG产品中的FXIa水平进行定量。这应有助于规范IG产品中血栓形成潜力的测量，并防止显示高促凝活性的产品分发供患者使用。需要进一步研究以解决IG产品特异性基质对检测性能的影响。
