Effect of hormone replacement therapy on the endogenous thrombin potential

Hormone replacement therapy (HRT) has been associated with a two- to fourfold increased risk of venous thromboembolism (VTE) in recent studies. However, thel explanation for this increase thrombogenicity is still unknown. The endogenous thrombir potential (ETP), which is a measure of the effect of activated protein C (APC) on thrombir generation when the extrinsic coagulation pathway is activated, reflects the activity of thel protein C pathway. Results of the ETP assay are expressed by a sensitivity ratio (APC-i sr), which gives values in the opposite direction compared to those of the aPTT-basec activated protein C resistance (APCR) assay. To evaluate the effect of HRTon ETP, we| analysed plasma samples of 71 women with suspected first VTE who had the disease! excluded. To avoid a confounding effect, patients with positive APCR or Factor V Leider mutation as well as patients with malignancy were excluded from the analysis. Among the population studied, 20 women were taking estrogen therapy alone while 51 women wert non-users. Results of ETP assay were expressed as the APC-sr. The mean and standarc deviation (SD) were calculated for each group. Comparison of means between groups was then performed by a t-test. Mean and median APC-sr were 2.90 (SD: 0.83) and 2.89 respectively for women using HRT (estrogen alone) and 2.19 (SD: 0.94) and 2.04 respectively in women not using HRT. N Mean SD Median No Hormone 51 2.19 0.94 2.04 Estrogen 20 2.90 0.83 2.89 The t-test procedure for comparison of means revealed a significant difference betweerj groups (p=0.005). Because of a slight skewness of the distribution, we performed a non parametric test (Mann-Whitney test), which gave similar results (p=0.002). In conclusion our results show a significant increase in the ETP with the use of estrogen therapy which might be an indicator of its thrombogenicity. Further studies are required to confirm these results and to investigate whether patients with abnormal ETP are prone to thrombosis.