Monitoring heparin therapy--a role for the chromogenic assay.

Heparin therapy was evaluated by simultaneous determinations of the activated partial thromboplastin time (APTT), and plasma heparin levels by chromogenic assay. These tests showed good correlation (r = 0.73) in patients on heparin alone. However, in the presence of concurrent warfarin administration, r fell to 0.37, reflecting an additional warfarin effect upon the APTT. Furthermore, the studies confirmed the increased heparin requirement in patients with pulmonary embolization.