A Targeted LC-MS/MS–Based Quantitative Assay for Detecting Plasma Factor XIII A/B Subunit Deficiency

Factor XIII (FXIII) is a heterotetramer that plays a crucial role in the coagulation cascade, facilitating fibrin crosslinking to stabilize clots. Congenital or acquired deficiency of the FXIII A or B subunits can lead to prolonged bleeding. Existing enzyme-linked immunosorbent assay–based and latex agglutination assays for measuring FXIII are limited to detecting only the FXIIIA subunit of the complex. In this study, a targeted liquid chromatography–tandem mass spectrometry (LC-MS/MS) assay was developed and validated to accurately quantify both FXIIIA and FXIIIB subunits in plasma.