Diagnosing Hypogonadism with Testosterone Labs

Primary Laboratory Tests

Morning total testosterone levels should be measured on at least two separate days to account for natural variations, according to the American College of Clinical Endocrinologists 1, 2
Free testosterone measurement is a better index of gonadal status than total testosterone and should be measured when possible, as recommended by the Endocrine Society 3, 1
Sex Hormone Binding Globulin (SHBG) should be measured to calculate the free testosterone index (ratio of total testosterone/SHBG), as suggested by the European Society of Endocrinology 3, 1
Luteinizing hormone (LH) and Follicle-stimulating hormone (FSH) levels help distinguish between primary (hypergonadotropic) and secondary (hypogonadotropic) hypogonadism, according to the American College of Clinical Endocrinologists 1

A free testosterone index (total testosterone/SHBG ratio) <0.3 indicates hypogonadism, as reported by the European Society of Endocrinology 3
For values in the "grey zone" between 8-12 nmol/L (230-350 ng/dL), free testosterone or bioavailable testosterone measurement is essential, as recommended by the American College of Clinical Endocrinologists 2

Serum prolactin levels should be checked in patients with low testosterone combined with low or low/normal LH levels, according to the American College of Clinical Endocrinologists 1
Thyroid function tests should be performed to rule out thyroid disorders that may affect testosterone levels, as suggested by the European Society of Endocrinology 3
Bone function tests including corrected serum calcium and serum phosphate should be considered, especially if osteoporosis is suspected, as recommended by the European Society of Endocrinology 3
Consider measuring 25-OH vitamin D levels, particularly in patients at high risk of vitamin D deficiency, as suggested by the European Society of Endocrinology 3

Laboratory diagnosis must be correlated with clinical symptoms of hypogonadism, as testosterone deficiency requires both low testosterone levels AND symptoms/signs, according to the American College of Clinical Endocrinologists 2

Failing to obtain morning samples when testosterone levels are highest, as recommended by the American College of Clinical Endocrinologists 1
Not repeating testosterone measurements to confirm low levels, according to the American College of Clinical Endocrinologists 1
Failing to distinguish between primary and secondary hypogonadism, which require different management approaches, as recommended by the American College of Clinical Endocrinologists 1

In obese patients or those with altered SHBG levels, free testosterone measurement is particularly important as total testosterone may be misleadingly low, according to the American College of Clinical Endocrinologists 2
For patients with normal SHBG but reduced total testosterone, free testosterone measurement by equilibrium dialysis is recommended to determine if true testosterone deficiency exists, as suggested by the American College of Clinical Endocrinologists 2
Consider measuring total testosterone in patients with specific risk factors even without symptoms, including unexplained anemia, bone density loss, diabetes, HIV/AIDS, chronic narcotic or corticosteroid use, as recommended by the American College of Clinical Endocrinologists 2