How many days after administering testosterone replacement therapy (TRT) should testosterone levels be checked?

Timing of Testosterone Level Measurements After Testosterone Replacement Therapy

For patients on testosterone injections, testosterone levels should be measured midway between injections (typically 5-7 days after injection for standard testosterone cypionate or enanthate) to accurately assess treatment efficacy. 1

Initial Monitoring Timeline

• First follow-up visit should occur at 1-2 months after initiating testosterone replacement therapy to assess treatment efficacy and consider dose adjustments if needed 2, 1
• Testosterone levels should be formally tested 2-3 months after treatment initiation or after any dose change 1
• Subsequent monitoring visits should be performed at 3-6 month intervals for the first year, then yearly thereafter 2

Pharmacokinetics of Injectable Testosterone

• For intramuscular testosterone injections (cypionate or enanthate), peak serum testosterone levels occur 2-5 days post-injection 2
• Testosterone levels typically return to baseline by 10-14 days after injection 2, 1
• Injectable testosterone creates fluctuating serum testosterone levels with peaks and valleys between injections 1, 3

Optimal Timing for Blood Tests

• For standard testosterone cypionate or enanthate injections, measure levels midway between injections (typically day 5-7 for weekly injections) 1
• Clinicians must interpret blood test results based on the interval since the most recent injection 2
• Avoid measuring at peak (2-5 days post-injection) or trough (just before next injection) as these don't represent average exposure 1, 3

Target Levels and Dose Adjustments

• Target testosterone levels should be in the mid-to-upper normal range for optimal treatment response 2
• If clinical response is suboptimal and testosterone levels are in the low-normal range, the testosterone dosage should be increased 2, 1
• Recognize that peak serum testosterone levels may transiently rise above the upper limit of normal with standard injection therapy dosages 2

Monitoring Parameters Beyond Testosterone Levels

• At each follow-up visit, assess symptomatic response to treatment, voiding symptoms, and sleep apnea 2
• Physical examination should include a digital rectal examination 2
• Blood tests should measure serum testosterone, PSA levels, and hematocrit or hemoglobin level 2
• If hematocrit rises above the reference range, consider temporarily withholding testosterone therapy, reducing the dosage, or performing phlebotomy 2, 1

Differences Between Testosterone Formulations

• Long-acting injectable testosterone (undecanoate) has different monitoring requirements than standard cypionate/enanthate formulations 4
• Transdermal testosterone (gels/patches) provides more stable levels and can be measured at any time after reaching steady state 5, 6
• Oral testosterone undecanoate shows marked variability in absorption and requires more frequent monitoring 3