When should testosterone levels be checked during testosterone replacement therapy (TRT)?

When to Check Testosterone Levels During TRT

Measure testosterone levels 2-3 months after starting therapy or after any dose change, with the first clinical follow-up at 1-2 months to assess symptoms and consider dose adjustments. 1, 2

Initial Monitoring Schedule

• First clinical visit: 1-2 months after starting TRT to evaluate symptomatic response and consider dose modifications 1, 2
• First testosterone level measurement: 2-3 months after treatment initiation or any dose adjustment, allowing adequate time for steady-state levels 1, 2
• Subsequent monitoring: Every 3-6 months during the first year, then annually thereafter 1, 2

Timing Based on Formulation Type

Injectable Testosterone (Cypionate/Enanthate)

The pharmacokinetics of injectable testosterone create significant fluctuations that directly impact when you should draw blood:

• Peak levels occur: 2-5 days post-injection 1, 2
• Return to baseline: 10-14 days post-injection 1, 2

For weekly injections: Draw blood at day 5-7 (midpoint between injections) to capture average therapeutic levels 1, 2

For biweekly injections: Two options exist:

• Draw at trough (just before next injection) to ensure levels don't drop below therapeutic range 2
• Draw at midpoint (day 7) to assess mid-cycle levels 2

The midpoint measurement is generally preferred as it provides a more representative assessment of treatment efficacy rather than capturing the lowest point 1, 2

Transdermal Testosterone Gel

• Measure at both peak (+2 hours post-application) and trough (+23 hours post-application) to ensure adequate levels throughout the day 3
• Research demonstrates that 70% of patients achieve adequate levels at +2 hours, but only 37% maintain therapeutic levels at +23 hours, highlighting the importance of checking both timepoints 3

Target Levels and Dose Adjustments

• Target range: Mid-to-upper normal range (approximately 500-600 ng/dL) for optimal treatment response 2
• If levels are low-normal with suboptimal clinical response: Increase the testosterone dose 1, 2
• Always interpret results based on: The interval since the most recent injection and the specific formulation's pharmacokinetics 1, 2

Additional Monitoring Parameters at Each Visit

Beyond testosterone levels, comprehensive monitoring should include:

• Hematocrit/hemoglobin: At every follow-up visit, with intervention if hematocrit >54% 2
• PSA levels: Baseline and ongoing monitoring in men over 40 2
• Clinical assessment: Symptomatic response, voiding symptoms, sleep apnea 1, 2
• Physical examination: Including digital rectal examination 1, 2

Common Pitfalls to Avoid

• Drawing blood at the wrong time: For injectable testosterone, measuring at peak (2-5 days post-injection) will falsely suggest adequate dosing, while measuring at trough may underestimate average levels 1, 2
• Inadequate follow-up testing: Real-world data shows only 36% of men receive follow-up testosterone measurements after starting TRT, and 49% of those with low pre-treatment levels remain biochemically hypogonadal on therapy, suggesting non-compliance or inadequate dosing 4
• Using different laboratories: All PSA and testosterone values should ideally be obtained using the same assay at the same laboratory for consistency 1
• Testing too early: Measuring before 2-3 months doesn't allow sufficient time for steady-state levels 1, 2