In an article published in Thrombosis Research, a team at the Mayo Clinic detailed the diagnosis, management, and outcomes of patients with autoimmune Factor V (FV) inhibitors.

In this retrospective study, researchers acquired data from their laboratory database for patients who received FV inhibitor care and testing from January 1999 to February 2017. Patients were separated into 2 groups: those who received clinical care at the clinic and those who underwent FV inhibitor evaluation only.

For the 8 FV inhibitor-positive patients who received care at the clinic, the median age of presentation was 68.7 years (44.4 – 84.6; 4 female). Two patients did not present bleeding symptoms. All of the patients had comorbidities and possible predisposing factors: 6 patients received antibiotics prior to developing a FV inhibitor, 1 patient had an amyloid-associated FV inhibitor, and all patients had prolonged prothrombin time (PT; range 16.4-90.2 s) and activated partial PT (aPTT; range 35-133 s). The patient with the highest inhibitor titer (16 BU) required the most aggressive treatment to stabilize bleeding. All patients with inhibitor titer greater than 5 BU (3 patients) had bleeding symptoms.

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Two patients were lost to follow up. PT and aPTT normalized within 12 to 27 days for 3 patients; hemostatic management of these patients consisted of observation (1 patient), fresh frozen plasma and recombinant factor VIIa (1 patient), and platelet transfusion, fresh frozen plasma, and factor eight inhibitor bypassing activity (1 patient). Three patients died within 30 days of diagnosis.

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Of the 76 patients who underwent FV inhibitor evaluation, 26 (34.2%) had positive FV inhibitor screens, 14 (18.4%) had equivocal screens, and 36 (47.4%) had negative screens. Inhibitor titer ranged from less than 1 to 279 BU and was negatively correlated with FV activity (Spearman coefficient: -0.71, P <.0001).

“This study supports the notion that clinical symptoms, not FV activity and inhibitor titer level, should guide management,” concluded the authors.


Sridharan M, Fylling KA, Ashrani AA, et al. Clinical and laboratory diagnosis of autoimmune factor V inhibitors: A single institutional experience [published online September 5, 2018]. Thromb Res. doi:10.1016/j.thromres.2018.09.044