The utility of the dilute prothrombin time in the interpretation of antiphospholipid syndrome testing.

Objectives: To evaluate the utility of the dilute prothrombin time (DPT) in diagnosing antiphospholipid syndrome (APS), alone and when paired with the dilute Russell viper venom time (DRVVT).

Methods: Dilute prothrombin time and DRVVT testing was performed on plasma samples spiked with apixaban or rivaroxaban, or depleted of vitamin K-dependent clotting factors. A retrospective analysis of all functional APS testing results over a 44-month period at the University of Chicago Medical Center was performed.