Abstract Disclosure: G. Le: None. S. Pinkson: None. J. Trejo: None. D. Tripathy: None. Long-term Effects of Gender Affirming Hormone Therapy (GAHT) on Lipid Profile There is differential effect of long-term Estrogen and Testosterone therapy on lipid profile. While oral estradiol therapy in post-menopausal women has been associated with increased serum triglyceride and HDL, testosterone therapy in hypogonadal men decreases total cholesterol, LDL and HDL cholesterol. However, the long-term effects of Estrogen and Testosterone on lipid profile in transgender patients are not clear. We conducted a retrospective study to analyze the long-term effects of GAHT in transgender men and women followed in Endocrinology Clinic at Veterans Affairs Hospital. 36 transgender men (age 38 ± 2 years, on IM Testosterone cypionate) and 54 transgender women (age 46 ± 2 years, 36 on E2 tablet, 12 on patch, 6 on IM) were followed for 46 ± 5 months and 61 ± 5 months, respectively. Total cholesterol, triglyceride, HDL, LDL cholesterol, systolic and diastolic blood pressures, and BMI were compared before and after initiation of therapy. As expected, following GAHT, total testosterone was higher (546 ± 48 vs. 35 ± 9 ng/dL, P<0.001) in transgender men; in transgender women, serum E2 was higher (110 ± 9 vs. 26 ± 2 pg/dL, P<0.001) and total testosterone was suppressed (444 ± 29 ng/dL vs. 66 ± 13 ng/dL). In transgender men, after a follow-up period of approximately 4 years, there were no significant changes in lipid profile (total cholesterol 178 ± 8 vs. 175 ± 8 mg/dL, triglyceride 121 ± 4 vs 134 ± 12 mg/dL, HDL 47 ± 2 vs. 44 ± 2 mg/dL, LDL 107 ± 7 vs. 106 ± 8 mg/dL, all p=NS). Similarly in transgender women, no difference in lipid profile (total cholesterol 170 ± 5 vs. 175 ± 4 mg/dL, triglyceride 118 ± 7 vs 140 ± 9 mg/dL, HDL 49 ± 2 vs. 53 ± 3 mg/dL, LDL 99 ± 4 vs. 97 ± 4 mg/dL, all p=NS) was observed after 5 years of GAHT. There were no differences in lipid profile regardless of E2 tablet, patch or IM therapy. In transgender men, there was an increase in diastolic blood pressure (72 ± 3 vs. 76 ± 2 mmHg, P<0.05) while in transgender women there was decrease in systolic blood pressure (124 ± 2 vs. 118 ± 2 mmHg, p<0.005), and slight increase in BMI (28 ± 0.9 vs. 30 ± 1 kg.m2, P<0.005). In conclusion, long-term testosterone therapy in transgender men and estrogen therapy in transgender women was not associated with worsening lipid profile. Estrogen therapy was associated with lower BP in transgender women and testosterone therapy led to higher BP in transgender men. Presentation: 6/2/2024