What is the appropriate order for testing testosterone levels?

Appropriate Order for Testing Testosterone Levels

Morning testosterone testing between 8-11 AM is recommended as the standard for all men, particularly those under 45 years of age, while men over 45 years can have reliable testosterone measurements taken any time before 2 PM. 1

Timing of Testosterone Testing

• For men under 45 years: Draw blood as close to 7-8 AM as possible due to significant diurnal variation

  • Total testosterone levels can decrease by 15% between morning and afternoon in younger men 2, 3
  • This timing is critical as misleading results may occur later in the day

• For men over 45 years: Blood can be drawn any time before 2 PM

  • Research shows minimal clinically significant variation in testosterone levels throughout the day in this age group 2, 4
  • Men with low testosterone often lack diurnal variation regardless of age 3

Recommended Testing Protocol

1. Initial Testing:

   • Measure morning total testosterone (TT) as the first diagnostic test 1, 5
   • Patient should be fasting for optimal results 5
   • Use reliable assay methods (liquid chromatography tandem mass spectrometry preferred) 5, 6

2. Follow-up Testing:

   • If initial results are borderline or inconclusive, repeat the measurement on a different day at the same time 1
   • For borderline cases, consider measuring free testosterone using calculations based on total testosterone, sex hormone binding globulin (SHBG), and albumin concentrations 1

Special Considerations

• For men with diabetes: Morning total testosterone measurement is specifically recommended when symptoms of hypogonadism are present 1

• For men with obesity: Be aware that obesity is a major confounder in testosterone level interpretation 1

  • Higher BMI correlates with lower testosterone levels and may require additional testing considerations

• For men with erectile dysfunction: Testosterone testing is a primary indication, especially in those for whom PDE5 inhibitor therapy has failed 1

Testing Methods

• Gold standard for total testosterone: Mass spectrometry 6
• Gold standard for free testosterone: Equilibrium dialysis followed by direct assessment 6
• Avoid: Direct immunoassays for free testosterone due to reliability issues 5, 6

Common Pitfalls to Avoid

1. Ignoring time of day for younger men (under 45) - can lead to false low readings
2. Failing to repeat borderline results - single measurements may not be representative
3. Not considering binding protein alterations - total testosterone may be normal while free testosterone is abnormal
4. Using unreliable laboratory methods - ensure the laboratory uses validated assays and participates in quality control programs
5. Not accounting for obesity when interpreting results - can significantly affect testosterone levels

By following these guidelines for testosterone testing, you can ensure accurate diagnosis and appropriate management of patients with suspected testosterone abnormalities.