Short-term thromboembolism risk and coagulation profiles among Thai transmasculine individuals receiving testosterone therapy: a quasi-experimental study

While the use of gender-affirming hormone therapy is steadily increasing, safety data specific to Asian transgender populations remain limited. This study aimed to evaluate the changes in activated protein C resistance and global coagulation profiles following a short-term testosterone injection among Thai testosterone-naïve, transmasculine individuals. Participants were enrolled and received 150 mg of testosterone enanthate intramuscularly every 2 weeks for total 14 weeks. Blood samples were collected at baseline and week 13 (mid-interval) to assess median change in APC sensitivity ratio (APCsr), coagulation markers and natural anticoagulant levels, alongside hematological, biochemical, and hormonal assessments. A total 29 participants were recruited. Median APCsr remained unchanged (from 2.77 [interquartile range [IQR] 2.70–2.85] at baseline to 2.78 [IQR 2.67–2.85] at week 13 [ p = 0.829]). The overall hemostatic shift was heterogeneous. Subgroup analysis according to total testosterone levels did not exhibit significant trend toward procoagulative change. APCsr did not significantly correlate with hormonal profiles. In predictive modeling, estradiol positively correlated with factor IX and fibrinogen levels, whereas rising hematocrit predicted natural anticoagulant levels. Short-term administration of testosterone enanthate did not alter the baseline risk of venous thromboembolism among Thai transmasculine population. Trial registration : The Thai Clinical Trials Registry–TCTR20250826006.