ACTIVATED CLOTTING TIME VERSUS ACTIVATED PARTIAL THROMBOPLASTIN TIME FOR THERAPEUTIC MONITORING OF HEPARIN

OBJECTIVE: TO compare and contrast the activated partial thromboplasti n time (aPTT) and the activated clotting time (ACT) for the therapeuti c monitoring of heparin therapy. DATA SOURCES: Relevant articles were identified through an English-language MEDLINE search from 1966 to 199 5. Additional sources were identified from the reference lists of thes e articles. STUDY SELECTION: Studies that investigated the use and lim itations of the individual assays and those offering direct comparison s were chosen for review. DATA EXTRACTION: Features demonstrating clin ical applications and limitations of the aPTT and the ACT were extract ed. Where possible, data suggesting preferential application of either assay also were extracted. DATA SYNTHESIS: Both the aPTT and ACT are clinically useful for the monitoring of heparin therapy. The aPTT is u sed more frequently for routine monitoring; the ACT is used in special ized situations requiring large heparin doses. The ACT is typically pe rformed at bedside and is capable of yielding results rapidly and perh aps at a lower cost than an aPTT performed by a central laboratory. Mo st practitioners are familiar with the central laboratory aPTT. A beds ide aPTT device is available, but is not yet in widespread clinical us e. Both assay techniques are subject to various limitations. CONCLUSIO NS: The ACT is theoretically equally as useful as the aPTT for the rou tine monitoring of heparin therapy, but has not been well-studied. The ACT appears more useful in situations in which high serum concentrati ons of heparin are required. Further cost-effectiveness and clinical o utcome studies directly comparing the ACT and the aPTT in specific cli nical situations are needed.