Laboratory control of continuous intravenous heparin therapy with Howel time and activated partial thromboplastin time. A prospective, randomized and blind study.

Although heparin has been used extensively to treat Deep Venous Thrombosis (DVT) and arterial ischemia (AI), controversy still exists regarding optimal dosage and the need for monitoring. Different authors have employed various test with variable results. Others, however, persist in giving heparin without laboratory control. This study was made in order to compare, in a prospective, randomized and blind manner, two coagulation tests, namely: Howel Time (HT) and Activated Partial Thromboplastin Time (APTT), in controlling the dose of heparin given by continuous intravenous infusion in DVT and AI. Our results show no significant difference in complications and failures of the therapy with either test, although significantly higher doses of heparin were needed to maintain APTT within therapeutic range than those needed to keep HT within a similar range.