May present with features of testosterone deficiency and/or infertility.
When caused by pituitary macro-adenoma, patients may have additional symptoms due to mass effects, such as headaches or peripheral visual disturbance. There may also be signs and symptoms of other pituitary hormone deficiencies.
Early morning serum total testosterone level below 10.4 nanomol/L (<300 nanograms/dL) on at least two separate occasions in a symptomatic man generally confers the diagnosis of hypogonadism.
Testosterone should be measured in all men with erectile dysfunction.
Measurement of the gonadotrophins (LH and FSH) distinguishes between a primary and a secondary cause.
The aim of testosterone therapy is to achieve serum testosterone levels within the normal physiological range with dose adjustment to have the maximum effect on alleviation of symptoms.
Hypogonadism in males is a clinical syndrome that comprises symptoms and/or signs, along with biochemical evidence of testosterone deficiency. 
The male gonads (testes) have 2 primary functions: testosterone production (by the Leydig cells) and spermatogenesis (by the spermatogenic and Sertoli cells in the seminiferous tubules). Hypogonadism in men occurs where there is dysfunction in the normal physiological mechanism of the hypothalamic-pituitary-gonadal axis that results in a decreased ability to carry out either of these functions.
Assistant Professor of Surgery
Division of Urology
Albany Medical College
CW has worked as a consultant for Coloplast, and as an investigator for Auxilium Pharmaceuticals, Mereo BioPharma, PROCEPT BioRobotics, and Repros; and he is a paid reviewer at Oakstone Publishing and BMJ Best Practice. CW also has a family member who is an employee at Bristol-Myers Squibb.
Dr Charles Welliver would like to gratefully acknowledge Matthew Aoun for his help with updating this topic. He would also like to acknowledge Dr T. Hugh Jones, Dr Milena Braga-Basaria, and Dr Shehzad Basaria, previous contributors to this monograph. THJ and SB are authors of references cited in this topic. MB declared that she had no competing interests.
Department of Internal Medicine
University of Texas Medical Branch
RJU declares that he has no competing interests.
Oxford Centre for Diabetes, Endocrinology and Metabolism
NK declares that she has no competing interests.
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