How does hrt cause blood clots

Studies have also suggested a dose-related effect, suggesting high-dose estrogen therapy is associated with a greater increased risk of venous thrombosis than low-dose preparations. Comparisons between oral and transdermal HRT have shown a significant difference in the relative risk of venous thrombosis OR, 4.

The presence of thrombophilia, particularly factor V Leiden, further amplifies the risk of venous thrombosis in women using HRT OR, The presence of other risk factors, such as increasing age and being overweight, were all shown to be associated with a further increase in the risk of venous thrombosis.

Conclusions: Recent studies have confirmed that current users of HRT are at increased risk of venous thrombosis. The increase in risk has been shown to vary according to duration of use, with the risk being greatest during the first year of use. Studies published in and suggested that HRT can increase the risk of DVT two- or threefold, which I discuss in more detail below. HRT can be administered as oral tablets, dermal patches, creams or suppositories. A case-control study published in included cases of DVT.

These women were compared with controls similar women without DVT. Participants were asked if there was any immobilisation or smoking during the three-month period before the DVT occurred; as these may also increase risk of blood clots. Overall, yes. Current use of hormone therapy was reported by cases with deep vein thrombosis Use of combined hormone therapy estrogen plus progestin was associated with an almost threefold risk of DVT.

Use of estrogen only was associated with a tiny and imprecise increased risk increase. Again, yes. Similar to previous studies, an increased risk of DVT was observed with the use of oral but not with transdermal estrogen patches. The study assessed GP prescription records of 80, women aged years who had developed blood clots and , women who had not. Similar to the previous study, HRT prescriptions were assessed in the recent day period before the blood clots occurred.

Again, this study found women who had used HRT absorbed through the skin, did not have an increased risk of blood clots. Although all treatments are effective in managing menopausal symptoms, an increased risk of venous thromboembolism blood clots is a rare, but serious, known side effect.

A recently issued guideline from the National Institute for Health and Care Excellence NICE stressed that research results from studies trying to estimate the risk of developing blood clots as a result of HRT are still not clear, and that findings to date were not a reliable basis for decision-making by doctors or patients. The Nottingham study aimed to provide clarity on the subject by identifying and comparing venous thromboembolism risks for all forms of HRT treatment used in the UK.

The study used data from the two largest UK primary care databases QResearch and CPRD , which contain patient records from more than 2, English GP practices and associated hospital records over an year period to investigate real-life use and risks of blood clots for all types of HRT treatments. The researchers compared the treatment prescription records of all women who developed blood clots with those for a group of women who did not.

To ensure that the results properly reflected the effects of the different therapies, the study took into account other relevant health conditions and patient characteristics, which might have affected the risk of developing blood clots. For tablet treatments, the risk was found to differ for two types of oestrogens. Both for single and combined hormone treatments, the risk of blood clots was 15 per cent higher for the treatments containing oestrogen manufactured from horse urine than for the synthetic oestradiol.

However, women who were using HRT in patch, gel or cream form were not found to be at risk, even at higher doses. The results of the study could also be helpful to agencies such as NICE in the development of new best-practice guidelines. Dr Vinogradova says: "Our study has shown that, for oral treatments, different tablets are associated with different risks of developing blood clots, depending on the active components.

It has also confirmed that risks of thrombosis for patients using HRT treatments other than tablets patches or gels is very low. This lower risk has been known for more than ten years and - although patches or gels may not be acceptable in some circumstances - it was surprising to find that only 20 per cent of HRT prescriptions to date have been for non-oral treatments.