# A Case Report of Non‐Neutralizing Acquired Factor V Inhibitor Mimicking Deficiency: Diagnostic Challenges and Therapeutic Implications

## TL;DR

An 81-year-old man with a rare coagulation disorder was found to have a non-neutralizing Factor V inhibitor, leading to diagnostic and treatment challenges that were eventually resolved with immunosuppressive therapy.

## Contribution

This case report highlights the diagnostic and therapeutic challenges of non-neutralizing Factor V inhibitors, which are rarely documented in clinical literature.

## Key findings

- Initial tests suggested Factor V deficiency, but standard treatments failed, indicating a non-neutralizing inhibitor.
- Platelet transfusions and immunosuppressive therapy with rituximab and IVIG normalized Factor V levels and coagulation parameters.
- The case underscores the importance of integrating clinical and laboratory data to manage rare coagulopathies effectively.

## Abstract

Acquired Factor V (FV) deficiency due to inhibitors is a rare coagulopathy that presents significant diagnostic and therapeutic challenges. We report the case of an 81‐year‐old male with persistent gross hematuria and severe coagulopathy, marked by prolonged prothrombin time (PT), activated partial thromboplastin time (aPTT), and critically low FV activity (< 1%). Initial mixing studies corrected the coagulation abnormalities, suggesting a deficiency rather than an inhibitor; however, standard therapies failed. Fresh frozen plasma (FFP) did not elevate FV levels, and recombinant activated Factor VII (rFVIIa) did not resolve his symptoms, raising suspicion for a non‐neutralizing inhibitor that depletes FV by increasing clearance. Clinical improvement was achieved with platelet transfusions, and his FV level normalized after treatment with rituximab and intravenous immunoglobulin (IVIG). PT and aPTT improved from 60 and > 200 to 12 and 32, respectively. It has remained normal with subsequent maintenance immunosuppression with rituximab. This case illustrates the diagnostic complexity created by non‐neutralizing FV inhibitors, which accelerate factor clearance without directly impairing activity. It highlights the critical need for integrating clinical and laboratory findings to guide tailored treatment in managing rare coagulopathies.