What labs do I order to test someone's testosterone levels?

Laboratory Testing for Testosterone Levels

To test someone's testosterone levels, order early morning total testosterone measurements on two separate occasions, as this is the recommended initial diagnostic approach for accurate assessment.

Primary Testing Protocol

• Order total testosterone level measured in the early morning (before 10 AM) to account for diurnal variation in testosterone production 1
• Repeat the total testosterone measurement on a separate morning to confirm results, as there can be significant intra-individual variability 1
• Use a reliable assay and preferably the same laboratory with the same method/instrumentation for both measurements 1
• The threshold for low testosterone is defined as consistently <300 ng/dL on at least two measurements 1

Additional Testing When Total Testosterone is Low

• Measure serum luteinizing hormone (LH) levels to determine if hypogonadism is primary (testicular) or secondary (pituitary/hypothalamic) 1
• Measure serum prolactin levels in patients with low testosterone combined with low or low/normal LH levels 1
• Consider referral for endocrine evaluation if prolactin levels are persistently elevated without clear cause 1

When to Consider Free Testosterone Testing

• Order free testosterone testing when:

  • The patient has conditions that may affect sex hormone-binding globulin (SHBG) levels, such as obesity 2
  • Total testosterone is near the lower limit of normal 3, 4
  • There is clinical suspicion of testosterone deficiency despite borderline total testosterone levels 5

• Free testosterone is best measured by equilibrium dialysis method, which is more accurate than calculated or analog methods 2, 4

• Be aware that free testosterone assays available at most local laboratories using analog methods have limited reliability 1

Special Considerations

• Fasting state may affect testosterone levels, particularly in women, though guidelines for men do not specifically require fasting 6
• Total testosterone between 280 and 350 ng/dL is not sensitive enough to reliably exclude hypogonadism; total testosterone must exceed 350 to 400 ng/dL to reliably predict normal free testosterone 5
• Consider testosterone testing in patients with specific risk factors even in the absence of symptoms: unexplained anemia, bone density loss, diabetes, exposure to chemotherapy, testicular radiation, HIV/AIDS, chronic narcotic use, male infertility, pituitary dysfunction, and chronic corticosteroid use 1

Common Pitfalls to Avoid

• Do not rely on screening questionnaires as substitutes for laboratory testing due to their variable sensitivity and specificity 1
• Do not make a diagnosis of testosterone deficiency based on a single measurement due to significant day-to-day variability 1
• Avoid using analog free testosterone assays when possible, as they have limited reliability compared to equilibrium dialysis 1, 4
• Do not diagnose testosterone deficiency based solely on laboratory values without corresponding symptoms and signs 1