[3] The presence of both prolonged PT and aPTT (not corrected after mixing with normal plasma), and an isolated FV deficiency, in a patient with a negative personal/familial bleeding history, leads to the initial diagnosis of acquired FV inhibitor. Inhibitors directed against factor V (FV) occur seldom, primarily in the elderly, and the clinical presentation varies from asymptomatic laboratory abnormalities to life-threatening bleedings. [1][2] Acquired FV inhibitors usually are immunoglobulin of the G class (IgG) directed to the binding site for phosphatidylserine (present in the second C-type domain of the light chain of FV). [Extracted from the article]