What laboratory test is most useful to confirm a suspected Factor V deficiency?

The most appropriate test to confirm a suspected Factor V deficiency is the Factor activity assay. This specialized assay quantitatively measures the activity of Factor V in the patient’s plasma. If there is a deficiency or dysfunction of Factor V, the assay will reflect a significantly reduced level of activity, providing clear evidence of a Factor V deficiency.

When considering other tests, while the prothrombin time (PT) and activated partial thromboplastin time (PTT) tests can indicate issues with the coagulation pathway, they do not specifically confirm a Factor V deficiency. PT primarily assesses the extrinsic and common pathways, and PTT evaluates the intrinsic and common pathways, but neither can isolate the specific factor responsible for the deficiency. Similarly, the thrombin time (TT) is used to evaluate the conversion of fibrinogen to fibrin but does not provide direct information about Factor V levels.

Thus, the Factor activity assay is the definitive test for diagnosing Factor V deficiency, allowing for an accurate assessment of this specific deficiency in the context of bleeding disorders.