When to Repeat Testosterone Levels After Initiating TRT
Measure testosterone levels at 1-2 months after starting therapy for efficacy assessment and dose adjustment, then every 3-6 months during the first year, and annually thereafter. 1, 2
Initial Monitoring Timeline
The first testosterone level should be checked at 1-2 months (or more precisely, 2-3 months) after initiating TRT or after any dose change. 2, 3 This initial assessment is critical for determining whether the dose is adequate to achieve therapeutic testosterone levels in the mid-to-upper normal range (300-1,000 ng/dL). 2, 3
Timing Considerations Based on Formulation
For injectable testosterone (cypionate or enanthate):
- Measure levels midway between injections (typically day 5-7 for weekly injections) to get an accurate assessment, as peak levels occur 2-5 days post-injection with return to baseline by 10-14 days. 2
- Avoid measuring at peak (2-5 days post-injection) or trough (just before next injection) to prevent misleading results. 2
For topical testosterone gel:
- The FDA label specifies measuring morning, pre-dose serum testosterone approximately 14 days after initiation to ensure proper concentrations are achieved. 3
- If levels are below 300 ng/dL, increase from 50 mg to 100 mg daily (maximum dose). 3
Ongoing Monitoring Schedule
After the initial 1-2 month check, repeat testosterone levels every 3-6 months for the first year, then annually thereafter. 1, 2 This schedule applies regardless of formulation type.
At each monitoring visit, also measure:
- Hematocrit or hemoglobin (to detect polycythemia, which may require dose reduction or phlebotomy if elevated above reference range) 1, 2
- PSA levels (to monitor for prostate-related concerns) 1, 2
- Clinical response including symptom improvement, voiding symptoms, sleep apnea, and gynecomastia 1, 2
- Digital rectal examination 1
Critical Pitfalls to Avoid
Do not measure testosterone levels at random times relative to injection timing, as this will yield uninterpretable results given the significant fluctuations in serum levels with injectable formulations. 2 The pharmacokinetics create peaks and valleys that must be accounted for when interpreting results. 2
Do not wait longer than 2-3 months for the first follow-up, as suboptimal dosing may leave patients symptomatic unnecessarily, and supraphysiological dosing increases risks of polycythemia and other adverse effects. 2, 3
If clinical response is suboptimal despite testosterone levels in the low-normal range, increase the dose rather than accepting inadequate symptom control, while carefully monitoring for side effects. 2