The Laboratory Control of Intravenous Heparin Therapy

A laboratory protocol for the monitoring of continuous intravenous heparin therapy has been examined in the present study. More than 500 samplings were tested in the course of a six-month survey period, involving 113 heparinized patients. The procedure essentially invokes the aid of three simple and familiar test methods: (a) the thrombin clotting time (TCT), which selects those patients who show positive antithrombin effect from those who do not; (b) the fibrinogen titre (FbT), whereby free antithrombin may be assayed in those plasma samples selected by the TCT; and (c) the activated partial thromboplastin time (APTT), the use of which in this particular context has been suggested by other writers. A fourth test, the one-stage prothrombin time, while insensitive to heparin effect, is included as a routine check on unrelated coagulation defects which may not be detected by the other methods. It has been observed that the TCT is a reliable screening test, and that there is good correlation between the results of the APTT and FbT in the assessment of free antithrombin effect, and appropriate maintenance ranges for each parameter have been proposed.