Aghazadeh M, Pastuszak AW, Johnson WG, McIntyre MG, Hsieh TM, Lipshultz LI. Elevated Dihydrotestosterone is Associated with testosterone-Induced Erythrocytosis. J Urol. http://www.jurology.com/article/S0022-5347(15)00059-2/abstract INTRODUCTION: Erythrocytosis is the most common dose-limiting adverse effect of testosterone therapy (TTh), but the mechanisms of T-mediated erythropoiesis remain unclear. In this study, we examine risk factors for erythrocytosis associated with TTh. METHODS: Retrospective review of 179 hypogonadal men on TTh in a single andrology clinic was performed. Demographic data, TTh formulation and duration of treatment, and 5alpha reductase inhibitor (5ARI) use were assessed. Serum dihydrotestosterone (DHT), total T (TT), free T (FT), follicle stimulating hormone (FSH), luteinizing hormone (LH), Hematocrit (Hct), and lipid levels were extracted and changes during treatment determined. Spearman's rank correlation was used to identify relationships between change in Hct (DeltaHct) and study variables. RESULTS: Of 179 patients, 49 (27%) developed a >/=10% DeltaHct and 36 (20.1%) developed erythrocytosis (Hct >/=50%) at a median follow-up of 7 months. Topical gels were used by 41.3% of patients, injectable T by 52.5%, and subcutaneous pellets by 6.1%. More men who developed DeltaHct >/=10% used injectable T than men with DeltaHct <10% (65% vs. 48%, p=0.035), and were less likely to be on 5ARI (2% vs. 15%, p=0.017). Men with DeltaHct >/=10% had higher post-treatment DHT levels (605.0 vs. 436.0 ng/dL, p=0.017) and lower LH and FSH levels than men with DeltaHct <10%. Spearman's rank correlations yielded relationships between DeltaHct and post-treatment DHT (rho=0.258, p=0.001) and TT (rho=0.171, p=0.023). CONCLUSION: DHT may play a role in TTh-related erythrocytosis, and monitoring of DHT levels during TTh should be considered. In men who develop erythrocytosis, 5ARIs may be therapeutic.