Study designs of evaluations included in the review
Randomised controlled trials (RCTs) were eligible for inclusion.
Specific interventions included in the review
Studies comparing LMWH with UFH of any type, preparation and route of administration for venous thromboembolism were eligible for inclusion if the planned follow-up was the same for LMWH and UFH. The specific thrombolytic drug therapies and doses were reported in the paper. All LMWH therapies were delivered subcutaneously, apart from one trial in which intravenous administration was used in addition to subcutaneous delivery.
Participants included in the review
Studies in patients with objectively diagnosed PE or DVT were eligible for inclusion. Objective diagnosis included pulmonary angiography, contrast venography, duplex ultrasound, Doppler scan, ventilation-perfusion scan, and/or computed tomographic scanning.
Outcomes assessed in the review
Studies that reported heparin-induced thrombocytopenia and heparin-induced thrombocytopenia with thrombosis were eligible for inclusion. Studies were required to define thrombocytopenia objectively, screen and measure platelet counts, and compare rates of thrombocytopenia for LMWH with UFH in the initial treatment of PE or DVT. For the primary analyses, ‘thrombocytopenia’ during LMWH or UFH therapy was defined as the occurrence of platelet counts in the range of 80,000 to 120,000/microL, or a decrease of at least 50% from a previously measured platelet level. A secondary analysis included all definitions of thrombocytopenia.
How were decisions on the relevance of primary studies made?
Two reviewers independently assessed studies for inclusion and any disagreements were resolved by consensus.