Monitoring Unfractionated Heparin Therapy with Antifactor Xa Activity Results in Fewer Monitoring Tests and Dosage Changes than Monitoring with the Activated Partial Thromboplastin Time

Study Objective. To determine how much more costly it is to monitor unfractionated heparin (UFH) therapy by antifactor Xa heparin activity (HA) than by activated partial thromboplastin time (aPTT). Design. Prospective, randomized, unmasked, cohort, single‐center study. Setting. A 625‐bed, adults‐only, private teaching hospital. Patients. Two hundred sixty‐eight patients with a variety of indications for UFH therapy. Interventions. Patients were treated with UFH based on ideal weight (75 U/kg bolus, 20 U/kg initial infusion) and monitored by either HA or aPTT. Measurements and Main Results. After adjusting for gender, groups were equivalent in patient characteristics and UFH dosage. The HA group had fewer monitoring tests and dosage changes/24 hours than the aPTT group. These reductions neutralized much of the increased cost of the HA assay itself. Conclusion. Monitoring UFH therapy over 96 hours with an HA assay costs $4.37 more than monitoring with aPTT. This modest increase may be acceptable given other advantages of the HA assay.