State-of-the-Art Review : Monitoring of High-Dose Intravenous Heparin Therapy—A Contribution to the Safety of Heparin Monitoring

Abstract

Whenever unfractionated heparin (UFH) is administered i.v. in therapeutic doses, therapeutic drug monitoring of the anticoagulant response should be mandatory and the dose should be adjusted accordingly. UFH therapy is usually monitored by the activated partial thromboplastin time (APTT). A 1.5-to 2.5-fold prolongation of APTT has become generally accepted as an indicator of effective i.v. anticoagulation, but it has become common to recommend this ratio without testing the APTT reagents used for their heparin sensitivity and for their actual therapeutic APTT ratio (actual APTT: normal control APTT). Internal heparin sensitivity testing of APTT reagents is managed using heparin sensitivity curves obtained from heparin-spiked normal plasma pool.The most common APTT reagents in Austria and a newly developed double activated APTT reagent were tested for their heparin sensitivity and therapeutic ratios on different automated analyzers, depending on their optical and chemical conditions. Also, newly developed, commercially prepared heparin standards (0.19, 0.52, 0.86 IU heparin/ml plasma) were tested. APTT reagents differ in their heparin sensitivity and therapeutic ratio; variations in heparin sensitivity are also seen between different analyzers. Therefore, therapeutic ratio should regularly be checked and the literature should always state which APTT reagent was used on which instrument.