Laboratory Testing for Testosterone Levels

Primary Testing Protocol

• The American Urological Association recommends ordering total testosterone level measured in the early morning to account for diurnal variation in testosterone production 1, 2, 3
• Repeat the total testosterone measurement on a separate morning to confirm results, as there can be significant intra-individual variability 1, 2, 3
• Use a reliable assay and preferably the same laboratory with the same method/instrumentation for both measurements 1, 3
• The threshold for low testosterone is defined as consistently <300 ng/dL on at least two measurements 2, 3

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, 3
• Measure serum prolactin levels in patients with low testosterone combined with low or low/normal LH levels 1, 3
• 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 4
• Free testosterone is best measured by equilibrium dialysis method, which is more accurate than calculated or analog methods 4, 5

Special Considerations

• 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, 3, 6

Common Pitfalls to Avoid

• Do not rely on screening questionnaires as substitutes for laboratory testing due to their variable sensitivity and specificity 1, 3
• Do not make a diagnosis of testosterone deficiency based on a single measurement due to significant day-to-day variability 1, 2, 3
• Avoid using analog free testosterone assays when possible, as they have limited reliability compared to equilibrium dialysis 5
• Do not diagnose testosterone deficiency based solely on laboratory values without corresponding symptoms and signs 2, 3