DOI: https://doi.org/10.36347/sjmcr.2026.v14i08.039

Pages: 1920-1925

Introduction: Specific acquired coagulation factor inhibitors may interfere with the interpretation of hemostasis laboratory investigations. Although widely used in routine practice, one-stage clotting assays for intrinsic pathway factors may generate misleading results suggestive of multiple factor deficiencies in the presence of circulating inhibitors. Objective: To investigate the impact of acquired anti-factor VIII (anti-FVIII) and anti-factor XI (anti-FXI) inhibitors on one-stage clotting assays of intrinsic pathway factors and to analyze the associated analytical biases. Materials and Methods: We retrospectively analyzed two longitudinal observations: one patient with an acquired anti-FVIII inhibitor and one patient with an acquired anti-FXI inhibitor. Each patient underwent two biological evaluations performed at different time points. Laboratory investigations included activated partial thromboplastin time (aPTT), mixing studies using pooled normal plasma, one-stage clotting assays for intrinsic pathway factors, and inhibitor detection and quantification using the Nijmegen-modified Bethesda assay. Results: In both cases, the presence of a specific inhibitor was associated with an apparent reduction in non-targeted coagulation factors, mimicking a multiple intrinsic pathway factor deficiency. In the anti-FVIII inhibitor case, the decrease in inhibitor titer during follow-up was associated with normalization of FIX, FXI, and FXII activities. In the anti-FXI inhibitor case, inhibitor disappearance was accompanied by improvement of abnormalities observed in other factor assays. These findings support an analytical interference rather than a true multiple factor deficiency. Conclusion: Acquired coagulation inhibitors may interfere with one-stage clotting assays and lead to diagnostic errors. An integrated interpretation combining clinical data, functional assays, inhibitor quantification, and alternative analytical methods is essential to avoid misdiagnosis.