The effects of postmenopausal hormone replacement therapy on hemostatic variables:: a meta-analysis of 46 studies

The aim of the study was to summarize and reanalyze all available data from the literature to study the overall effect of postmenopausal hormone replacement therapy (HRT) and its various forms on hemostatic variables. Studies were identified from literature searches by Medline and Index Medicus, review articles and personal communications. Reference lists of all articles were checked to find additional studies. Principal investigators were contacted and asked to provide additional data if required. Data were collected separately for each factor of the hemostatic system. Studies written in any language were included. Each collection of studies was analyzed using standard methods for meta-analysis. A total of 76 arms of 48 studies were eligible for analysis. This included 6119 women using HRT and 24 974 non-users. The age of investigated women was 40-68 years. HRT was associated with significantly decreased levels of fibrinogen, factor VIII, antithrombin III, and proteins C and S, but significantly increased plasminogen levels. HRT with estrogen alone or in combination with progestins, oral vs. transdermal regimens, different estrogen preparations and various progestins induced significantly different changes in many cases. In conclusion, HRT was associated with changes that could explain the increased rate of venous thrombotic events, and also with some changes that could account for beneficial vascular effects. Surprisingly, the addition of progestins induced favorable changes in many cases. Also, transdermal use was associated with more beneficial effects than oral regimens in some cases.