Study and Reporting Quality

The quality of the 22 included studies of men with erectile dysfunction who had their serum levels of testosterone, prolactin, luteinizing hormone (LH) and/or follicle-stimulating hormone (FSH) measured was assessed using QUADAS.⁴⁶

The QUADAS scores for each study are presented in Table C-2 (Appendix C).

About 60 percent of the studies provided an adequate description of population characteristics and inclusion/exclusion criteria.

Populations (Studies Reporting on Hypogonadism)

Twenty-one of the included studies measured testosterone serum levels in men with erectile dysfunction as total testosterone (TT) serum levels. ^{20, 38, 57–75} Two studies reported free testosterone (FT) serum levels, ^{59, 66} two studies reported calculated free testosterone (cFT) serum levels, ^{73, 74} and one study⁷³ calculated bioavailable testosterone (BT) serum levels.

Most studies recruited primary care clinic patients. In 10 studies participants were recruited from specialized clinics (urology, andrology, sexual dysfunction, and endocrinology clinics). Only 11 studies reported the use of a validated questionnaire to measure erectile dysfunction. The participants' mean age across studies ranged from 50 to 60 years. Important comorbidities such as hypertension, diabetes mellitus, and ischemic vascular disease were described in only 8 of the 22 studies.

Further details regarding the serum hormonal level measurements (e.g. time the serum was collected, cut-off values for positive/negative test results) are found in Table 1.

Prevalence of Hypogonadism (Total Serum Testosterone Levels)

The studies reporting prevalence rates of hypogonadism in ED patients are described in Table 2. All studies included men with a previous diagnosis of erectile dysfunction. The diagnosis of erectile dysfunction was given by a combination of clinical examination and validated questionnaires: the modified 5-item International Index of Erectile Function (IIEF-5) and Aging Males Symptoms (AMS).