When is the best time to check testosterone levels in a patient on injectable testosterone (testosterone) 100mg per week?

Optimal Timing for Testosterone Level Measurement on Injectable Testosterone

For a patient receiving 100mg testosterone cypionate or enanthate weekly, check testosterone levels midway between injections (day 3-4 after injection) to accurately assess therapeutic efficacy. 1

Understanding Injectable Testosterone Pharmacokinetics

The timing of blood draws is critical because injectable testosterone formulations create significant fluctuations in serum levels:

• Peak levels occur 2-5 days post-injection, with testosterone returning to baseline by 10-14 days after administration 1
• This creates the characteristic "peaks and valleys" pattern that distinguishes injectable testosterone from transdermal formulations 2
• For weekly 100mg dosing, measuring at the midpoint (day 3-4) captures a representative level that reflects average therapeutic exposure 1

Initial Monitoring Protocol

First assessment timeline:

• Schedule the first follow-up visit at 1-2 months after starting therapy to evaluate clinical response and tolerability 1
• Perform formal testosterone level measurement at 2-3 months after treatment initiation or after any dose adjustment 1
• This 2-3 month window allows achievement of steady-state kinetics 3

Subsequent monitoring:

• Continue monitoring every 3-6 months during the first year 1
• After stabilization, reduce frequency to yearly monitoring 1

Target Levels and Dose Adjustments

Therapeutic targets:

• Aim for testosterone levels in the mid-to-upper normal range when measured at the midpoint between injections 1
• If clinical response is suboptimal and midpoint levels are low-normal, increase the dose 1, 4
• If levels are supraphysiological or adverse effects occur, reduce the dose or temporarily discontinue 4

Critical Safety Monitoring Parameters

Beyond testosterone levels, monitor these parameters at each visit:

Hematologic monitoring:

• Check hematocrit/hemoglobin at baseline and all follow-up visits 1, 4
• If hematocrit rises above the reference range (>54%), consider temporarily withholding therapy, reducing dosage, or performing phlebotomy 1

Prostate monitoring:

• Measure PSA levels at each visit 1
• Perform prostate biopsy or refer to urology if PSA rises above 4.0 ng/mL 1
• Consider biopsy if PSA increases by ≥1.0 ng/mL within any 12-month period 1
• If PSA rises by 0.7-0.9 ng/mL in one year, repeat in 3-6 months and biopsy if further elevation occurs 1

Clinical assessment:

• Evaluate symptomatic response, voiding symptoms, and sleep apnea 1
• Perform digital rectal examination 1

Common Pitfalls to Avoid

Timing errors:

• Do not draw blood immediately after injection (will show supraphysiological levels) or just before the next dose (will show trough levels) 1
• Both timing extremes misrepresent the patient's average therapeutic exposure 2

Laboratory consistency:

• Use the same assay and preferably the same laboratory for all measurements to ensure comparability 1
• Testosterone levels should ideally show ≤10% variation when stable 1

Interpretation context:

• Always interpret results based on the interval since the most recent injection 1
• The pharmacokinetic profile differs substantially from longer-acting formulations like testosterone undecanoate, which has an 18-23 day half-life and requires different monitoring approaches 5, 6