Recommended Testosterone Labs for Diagnosing Hypogonadism
Morning serum total testosterone measurement is essential for diagnosis and should be repeated on at least two separate occasions to confirm low levels due to variability in assays. 1, 2
Primary Laboratory Tests
- Morning total testosterone levels (between 8-10 AM) should be measured on at least two separate days to account for natural variations 1, 3, 2
- Free testosterone measurement is a better index of gonadal status than total testosterone and should be measured when possible 4, 1
- Sex Hormone Binding Globulin (SHBG) should be measured to calculate the free testosterone index (ratio of total testosterone/SHBG) 4, 1
- Luteinizing hormone (LH) and Follicle-stimulating hormone (FSH) levels help distinguish between primary (hypergonadotropic) and secondary (hypogonadotropic) hypogonadism 1, 5
Interpretation Guidelines
- Total testosterone levels <8 nmol/L (<230 ng/dL) highly support a diagnosis of hypogonadism 6
- Total testosterone levels >12 nmol/L (>350 ng/dL) are likely to be normal 6
- For values in the "grey zone" between 8-12 nmol/L (230-350 ng/dL), free testosterone or bioavailable testosterone measurement is essential 3, 6
- A free testosterone index (total testosterone/SHBG ratio) <0.3 indicates hypogonadism 4
Additional Recommended Tests
- Serum prolactin levels should be checked in patients with low testosterone combined with low or low/normal LH levels 1
- Thyroid function tests should be performed to rule out thyroid disorders that may affect testosterone levels 4
- Bone function tests including corrected serum calcium and serum phosphate should be considered, especially if osteoporosis is suspected 4
- Consider measuring 25-OH vitamin D levels, particularly in patients at high risk of vitamin D deficiency 4
Clinical Correlation
- Laboratory diagnosis must be correlated with clinical symptoms of hypogonadism, as testosterone deficiency requires both low testosterone levels AND symptoms/signs 3, 5
- Be aware that traditional symptoms commonly attributed to hypogonadism (fatigue, depression) may not correlate well with testosterone levels 7
- Sexual symptoms (decreased libido) show better correlation with low testosterone levels than non-specific symptoms 7, 8
Common Pitfalls to Avoid
- Failing to obtain morning samples when testosterone levels are highest 1, 5
- Not repeating testosterone measurements to confirm low levels 1, 2
- Treating based on symptoms alone without laboratory confirmation of low testosterone levels 1, 7
- Not measuring free testosterone in cases with borderline low total testosterone, which can lead to misdiagnosis in up to 8.4% of men with sexual symptoms 8
- Failing to distinguish between primary and secondary hypogonadism, which require different management approaches 1, 9
Special Considerations
- In obese patients or those with altered SHBG levels, free testosterone measurement is particularly important as total testosterone may be misleadingly low 3, 8
- For patients with normal SHBG but reduced total testosterone, free testosterone measurement by equilibrium dialysis is recommended to determine if true testosterone deficiency exists 3
- 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 3