testosterone and Male to Female (MTF) patients on estrogen with or without testosterone blockers (ie. spironolactone). Patients with endocrine disorders that would predispose patients to altered metabolic profiles, including CAH and PCOS, were excluded. Previously recorded measurements of testosterone, estradiol, prolactin, and lipids were reviewed, as well as blood pressure, BMI, electrolytes, liver function tests, hemoglobin/ hematocrit, and hemoglobin A1c. Values reviewed were obtained from prior to the beginning of therapy (baseline), at 1-3 months after the initiation of therapy, at 4-6 months, and at 6 months and beyond. Repeated measures ANOVA models were used to evaluate the change in lab values and other metabolic markers over time.Results: A total of 116 adolescents were included in the study, including 72 FTM patients on testosterone and 44 MTF patients on estrogen. Of the 72 subjects on testosterone therapy, hemoglobin and hematocrit significantly increased at each subsequent visit. There was also a significant increase in BMI and lowering of HDL levels found at each visit. There was an increase in blood pressure, total cholesterol and LDL noted at the 3 month visit; however, these were not statistically significant and were noted to plateau after three months. Changes in AST/ALT, BUN/Cr, Estradiol, Prolactin, Triglycerides and HgbA1c were also not found to be statistically significant. Of note, testosterone doses above 50mg weekly were associated with a greater increase in hematocrit, systolic blood pressure and HDL compared to those receiving only 25mg every week.Of the 44 subjects on estrogen therapy, no statistically significant changes were noted to measured metabolic parameters over time. There was also no statistically significant difference in measured metabolic parameters among the different Methods of administration of estradiol (patch, oral or parenteral). There was also no significant change in potassium levels over time among the 38 subjects on concurrent spironolactone therapy.Conclusions: Testosterone use was associated with increased hematocrit levels; otherwise, cross-gender hormone administration in adolescents was not associated with significant differences in the selected metabolic parameters over time.Acknowledgement: Funding for statistical analysis is from the Medstar