What is the best time to check testosterone levels in a male patient and what other labs are recommended?

Best Time to Check Testosterone Levels and Recommended Labs

Testosterone levels should be measured in the morning (between 7-10 AM) after an overnight fast to obtain the most accurate results. 1, 2

Timing of Testosterone Testing

Morning Collection

• Testosterone has a circadian rhythm with highest levels in the morning (7-10 AM) 3
• Morning collection is recommended by guidelines for diagnostic purposes 2
• For men aged ≥45 years, the diurnal variation diminishes, making collection acceptable before 2 PM 4, 5

Fasting Status

• Research shows testosterone levels may decrease by approximately 30% at 60-120 minutes after food intake 2
• This post-prandial decrease could lead to false low values and overdiagnosis of hypogonadism
• However, some recent evidence suggests fasting status may not significantly affect total testosterone levels 6
• To ensure the most accurate results, fasting samples are still preferred for initial diagnosis

Recommended Laboratory Tests

Primary Tests

• Total testosterone (morning sample) - the cornerstone test for hypogonadism diagnosis 1
• Sex hormone-binding globulin (SHBG) - particularly important in men with total testosterone levels near the lower limit, as it is often low in diabetes 7
• Free testosterone calculation - provides additional information when SHBG is abnormal 1

Additional Tests When Hypogonadism Is Suspected

• Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) - to determine if hypogonadism is primary (testicular) or secondary (pituitary/hypothalamic) 7
• Complete blood count (CBC) with hematocrit - baseline measurement before initiating therapy 1
• Prostate-specific antigen (PSA) - baseline measurement before initiating therapy 7, 1
• Lipid profile - to assess cardiovascular risk 7, 1
• Hemoglobin A1c or fasting glucose - to screen for diabetes 7, 1

Monitoring During Testosterone Therapy

If testosterone therapy is initiated, the following monitoring schedule is recommended:

• Total testosterone levels: 3-6 months after starting therapy, then annually 7, 1

  • Target range: 450-600 ng/dL (mid-normal range) 1
  • For injectable testosterone: measure 2-5 days after injection (peak levels) 7

• Hematocrit: 3-6 months after starting therapy, then annually 7, 1

  • Discontinue therapy if hematocrit exceeds 54% 1

• PSA: 3-6 months after starting therapy, then annually 7, 1

  • Consider biopsy if PSA >4.0 ng/mL or increases >1.0 ng/mL/year 7, 1

Common Pitfalls and Caveats

• Testing in the afternoon may lead to falsely low testosterone levels, especially in younger men 3
• Non-fasting status may lead to falsely low testosterone levels 2
• Failure to measure SHBG in men with borderline low testosterone may miss cases of true hypogonadism 7
• Not considering age-related changes in diurnal variation (less pronounced in men ≥45 years) 5, 4
• Failing to monitor hematocrit during testosterone therapy, which can lead to polycythemia 7, 1
• Not monitoring PSA appropriately during testosterone therapy, which is essential for prostate cancer surveillance 7, 1

By following these recommendations, clinicians can accurately diagnose testosterone deficiency and safely monitor testosterone replacement therapy.