For an adult male with confirmed hypogonadism starting testosterone injections, when should the first laboratory recheck be performed and how often should labs be monitored thereafter?

Timing of Testosterone Level Recheck After Starting Injections

The first testosterone level should be checked 2–3 months after initiating testosterone injections, then every 6–12 months once stable levels are confirmed. 1, 2

Initial Monitoring Timeline

• First follow-up at 1–2 months to assess clinical response (particularly sexual function and libido) and consider dose escalation if symptoms persist with suboptimal levels 2, 3
• First laboratory recheck at 2–3 months after treatment initiation or any dose change to measure total testosterone, hematocrit, and PSA (in men >40 years) 1, 2, 3
• Subsequent monitoring every 3–6 months during the first year, then annually once stable 1, 2, 3

Optimal Timing for Blood Draw with Injectable Testosterone

For testosterone cypionate or enanthate injections, draw blood midway between injections (days 5–7 for weekly dosing, days 7–10 for bi-weekly dosing) targeting a mid-normal value of 500–600 ng/dL. 2, 3

Pharmacokinetic Rationale

• Peak serum testosterone occurs 2–5 days after injection, often transiently exceeding the upper limit of normal 2, 3, 4
• Testosterone returns to baseline by days 10–14 after injection 2, 3
• Drawing at the peak (days 2–5) will show supraphysiologic levels that do not reflect average exposure and may lead to inappropriate dose reduction 2
• Drawing at the trough (days 13–14) may show subtherapeutic levels, potentially leading to unnecessary dose escalation 2

Comprehensive Monitoring Parameters

At Each Visit (Every 3–6 Months First Year, Then Annually)

• Total testosterone (midway between injections for injectables) 1, 2, 3
• 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 first 6 months or >0.4 ng/mL per year thereafter 1, 2, 3
• Digital rectal examination to assess for prostate abnormalities 1, 2
• Clinical symptom response, particularly sexual function and libido 1, 2

Additional Baseline and Periodic Monitoring

• Lipid profile at baseline and periodically 2
• Fasting glucose/HbA1c at baseline 2
• Free testosterone only if total testosterone is borderline or patient is obese 2

Dose Adjustment Algorithm

• If clinical response is adequate, no dose adjustment is needed even if testosterone levels are in the low-normal range 2
• If clinical response is suboptimal AND testosterone levels are low-normal or below, increase the dose 2, 3
• If testosterone levels are consistently supraphysiologic at mid-interval, reduce the dose 2
• If maximal transdermal doses fail to achieve adequate levels, consider switching to intramuscular injections 2

Critical Pitfalls to Avoid

• Never draw testosterone at the peak (days 2–5), as this will show falsely elevated levels 2
• Never draw at the trough (days 13–14), as this may show falsely low levels 2
• Never skip hematocrit monitoring – injectable testosterone carries a 44% risk of erythrocytosis compared to 15% with transdermal preparations 2
• Never continue therapy beyond 12 months without documented improvement in sexual function – discontinue if no benefit despite achieving target testosterone levels 1, 2
• Approximately 50% of men on testosterone therapy never have their levels rechecked, representing a dangerous practice pattern 2

Long-Acting Formulations

For testosterone undecanoate (long-acting injectable):

• Initial injection, repeat at 4 weeks, then every 10–12 weeks thereafter 5, 6, 7
• Provides stable eugonadal levels for 10–11 weeks with zero-order kinetics 6, 8
• Check testosterone levels before the next scheduled injection once steady state is achieved (after 3–4 injections) 6, 7
• Substantially lower frequency of administration (4 injections per year) compared to cypionate/enanthate 5, 6, 7