SAT411 The Influence Of Gender Affirming Hormone Therapy On Markers Of Platelet Activation In Transgender Women

Disclosure: L.M. van Zijverden: None. M.H. Schutte: None. M.C. Madsen: None. J.J. van Diemen: None. C.M. Wiepjes: None. A. Thijs: None. M. den Heijer: None. Background: Transgender women often use hormone therapy to obtain body characteristics that comply with their experienced gender. This is important to improve quality of life and mental wellbeing. However, results from several studies show that trans women who use gender affirming hormones have an increased risk of cardiovascular disease (CVD) compared to cisgender women and men. The exact mechanisms that could explain this risk are yet undetermined. In general, platelet activation plays an important role in the development of CVD. This process might be influenced by feminizing hormone therapy, since platelets express estrogen receptors on their cell surface. The aim of our research was to gain insight in the role of platelet activation in CVD development in trans women. We therefore investigated the effect of estradiol on two markers of platelet activation: CD62p and CD63. Methods: In this prospective cohort study 17 trans women between 19 and 48 years old were included. They had no history of prior hormone therapy or known platelet disorders, and did not use antiplatelet medication. Treatment consisted of estradiol and anti-androgens. Blood was drawn at baseline and at 2, 12 and 52 weeks after the start of estradiol. We measured the percentage of platelets that were positive for activation markers CD62p and CD63. We also measured the fluorescence intensity of these markers. This is a way to measure the relative number of markers per platelet. These two measurements were then combined into a new outcome measure, called binding index (BI). Geometric means of the binding indices at each time point were calculated. We also calculated the percentage changes in binding index over time. Results: For CD62p, BI increased from 2.4 (95%CI 1.5, 3.7) at baseline to 4.6 (95%CI 2.0, 10.5) at week 2, reflecting a difference of 96% (95%CI -9, 318). After week 2, BI decreased to 2.6 (95%CI 1.3, 5.3) at week 12 and 1.4 (95%CI 1.0, 1.9) at week 52. The difference between week 52 compared to baseline was -40% (95%CI -69, 14). CD63 BI increased from 10.7 (95%CI 7.1, 16.1) at baseline with 32% (95%CI -32, 158) to 14.1 (95%CI 8.8, 22.8) at week 2. At week 12 and 52, BI was 13.1 (95%CI 7.4, 23.2) and 9.3 (95%CI 5.9, 14.6), respectively. The difference between week 52 compared to week 0 was -13% (95%CI -51, 53). Conclusions: The observed trends show an increase in binding index of both platelet activation markers directly after hormone therapy initiation. This could partially explain the increased rates of cardiovascular disease in transgender women in the early stages of their hormone therapy. However, we observe a decrease of CD62p and CD63 towards baseline values at twelve weeks of hormone therapy. This decrease continues until week 52. Hence, our results do not provide an explanation for an increased rate of CVD in trans women on the longer term. Presentation: Saturday, June 17, 2023