In this well-designed study, Hull et al1 showed 7 new episodes (6.8%) of venous thromboembolism in 103 patients who received intravenous heparin. None of the patients in the low-molecular-weight heparin (LMWH) group had a recurrence. Out of 7 patients, 1 patient had a subtherapeutic activated partial thromboplastin time while receiving heparin, and 2 patients had subtherapeutic prothrombin times before or at the time of a recurrent thromboembolic event. This may be a potential confounder.
Sharma GK. Is There Enough Evidence That Low-Molecular-Weight Heparin Is Superior to Unfractionated Heparin in Pulmonary Embolism?. Arch Intern Med. 2000;160(13):2061-2067. doi: