Laboratory Testing for Male with Low Libido

Initial Hormonal Assessment

The American Urological Association recommends measuring a morning total testosterone level using an accurate assay, and if levels are low or borderline, adding free testosterone, sex hormone-binding globulin (SHBG), and serum luteinizing hormone (LH) to guide further evaluation 1, 2
Low testosterone is generally defined as <300 ng/dL, though laboratory ranges vary from 300-800 ng/dL 1
If abnormal, repeat the test on a separate occasion to confirm the diagnosis before proceeding 1, 2
Measure free testosterone by equilibrium dialysis when total testosterone is low or borderline 1
Calculate or measure SHBG and albumin to distinguish true hypogonadism from SHBG-related changes 1, 3

Measure serum LH in all patients with confirmed low testosterone 2, 4
Low or inappropriately normal LH with low testosterone indicates secondary (central) hypogonadism from hypothalamic-pituitary dysfunction 1, 2
Elevated LH with low testosterone indicates primary (testicular) hypogonadism 1, 2
Measure serum prolactin only in men with low testosterone AND low/normal LH 2, 4
If prolactin is elevated, repeat the measurement to exclude spurious results 2, 4
Persistently elevated prolactin requires referral to endocrinology and evaluation for prolactinoma 2, 4
Men with total testosterone <150 ng/dL and low/normal LH should undergo pituitary MRI regardless of prolactin levels, as non-secreting adenomas may be present 2, 4

Measure FSH in men interested in fertility preservation 2, 4
Elevated FSH with low testosterone suggests impaired spermatogenesis and warrants consideration of semen analysis 2
Measure serum estradiol only if the patient presents with breast symptoms or gynecomastia prior to testosterone therapy 2, 4
Elevated baseline estradiol requires endocrinology referral 2, 4
Consider testosterone testing even in asymptomatic men with unexplained anemia, bone density loss, diabetes, obesity, HIV, chronic narcotic use, history of chemotherapy or testicular radiation, infertility, pituitary disorders, or chronic corticosteroid use 2, 4