When to Check Testosterone Levels After Starting Injections
For patients starting testosterone enanthate or cypionate injections, check the first testosterone level at 2–3 months after treatment initiation or after any dose change. 1, 2
Initial Monitoring Timeline
First follow-up visit should occur at 1–2 months to assess clinical response (particularly sexual function and libido) and consider dose escalation if symptoms persist with suboptimal levels 1, 2
First formal testosterone measurement at 2–3 months after starting therapy or after any dose adjustment 1, 2, 3
Subsequent monitoring every 3–6 months during the first year, then annually once stable levels are confirmed 1, 2, 3
Optimal Timing for Blood Draw
For injectable testosterone (cypionate or enanthate), draw blood midway between injections—typically days 5–7 after injection for weekly dosing or days 7–10 for every-2-week dosing—to capture average exposure rather than peak or trough values. 1, 2
Why This Timing Matters
Peak serum testosterone occurs 2–5 days after intramuscular injection, often transiently exceeding the upper limit of normal 1, 2, 3
Testosterone returns to baseline by days 10–14 after injection 1, 2
Drawing at the peak (days 2–5) will show supraphysiologic levels that don't reflect average exposure and may lead to inappropriate dose reduction 1
Drawing at the trough (days 13–14) may show subtherapeutic levels and lead to unnecessary dose escalation 1
Target Testosterone Levels
Aim for mid-normal testosterone concentrations of 500–600 ng/dL when measured at the midpoint between injections. 4, 1, 2
Dose Adjustment Algorithm
If clinical response is adequate (improved libido and sexual function), no dose adjustment is needed even if levels are in the low-normal range 1, 2
If clinical response is suboptimal AND testosterone levels are low-normal or below, increase the dose 1, 2
If levels are consistently supraphysiologic at midpoint, reduce the dose or shorten the injection interval 1
Additional Monitoring Parameters
Beyond testosterone levels, monitor the following at each visit:
Hematocrit/hemoglobin—withhold treatment if hematocrit >54% and consider phlebotomy in high-risk cases 1, 2, 3
PSA in men >40 years—refer to urology if PSA increases >1.0 ng/mL in the first 6 months or >0.4 ng/mL per year thereafter 1, 2, 3
Digital rectal examination to assess for prostate abnormalities 1, 2
Symptomatic response, particularly sexual function and libido, which show the most reliable improvement (standardized mean difference 0.35) 1
Common Pitfalls to Avoid
Never draw testosterone levels at the peak (days 2–5), as this will mislead you into reducing an appropriate dose 1
Never draw at the trough (days 13–14), as this may prompt unnecessary dose escalation 1
Nearly 50% of men on testosterone therapy never have their levels checked—this is dangerous practice 1
Don't adjust dose based on a single measurement; confirm with repeat testing if values are unexpected 1, 3
Don't ignore hematocrit monitoring—injectable testosterone carries a 44% risk of erythrocytosis (hematocrit >52%) compared to 15% with transdermal preparations 1
Long-Term Monitoring Schedule
Once stable testosterone levels are achieved:
Every 6–12 months: measure testosterone (midpoint between injections), hematocrit, and PSA (if >40 years) 1, 2, 3
Annually: perform digital rectal examination and assess symptomatic response 1, 2
At 12 months: if no improvement in sexual function despite achieving target testosterone levels, discontinue therapy to avoid unnecessary long-term exposure without benefit 1