Extremely Low Testosterone due to Relative Energy Deficiency in Sport: A Case Report

ABSTRACT Objective: Recognize extremely low testosterone due to hypothalamic dysfunction from overtraining syndrome in a male athlete with relative energy deficiency in sport (RED-S). Methods: Clinical and laboratory information are described. Results: A 20-year-old male division I collegiate swimmer was found to have strikingly low total, free, and bioavailable testosterone levels with normal sex hormone–binding globulin and inappropriately normal follicle-stimulating hormone and luteinizing hormone. Lab testing ruled out hyperprolactinemia and hypothyroidism as etiologies, and pituitary imaging was normal. A diagnosis of RED-S was made, and the patient worked with the sports medicine team to increase nutrition and modify physical activity. His repeat testosterone levels improved after minor weight gain and decreased training regimen and eventually returned to normal. Conclusion: Secondary hypogonadism with extremely low testosterone can be seen in male athletes with suspected RED-S. Abbreviation: RED-S = relative energy deficiency in sport