Retesting Low Testosterone
Low testosterone should be confirmed with a repeat morning measurement before making a diagnosis, and once confirmed and treatment is initiated, testosterone levels should be rechecked 2-3 months after starting therapy or any dose adjustment. 1, 2, 3
Initial Diagnostic Confirmation
Before any treatment decisions, the diagnosis of testosterone deficiency requires confirmation:
- Obtain a second morning total testosterone measurement (between 8-10 AM) to confirm the initial low result, as a single low reading is insufficient for diagnosis 4, 5, 3, 6
- Both measurements should be below 300 ng/dL to establish true testosterone deficiency 5, 3
- Morning timing is critical due to diurnal variation in testosterone production, with levels highest in early morning 5, 2
The 2018 AUA guideline and 2010 Endocrine Society guideline both emphasize that diagnosis requires both unequivocally low testosterone levels on repeat testing and consistent clinical symptoms (reduced libido, erectile dysfunction, fatigue, decreased muscle mass, reduced energy, impaired concentration) 4, 3, 6
Post-Treatment Monitoring Timeline
Once testosterone replacement therapy is initiated:
- Recheck testosterone levels at 2-3 months after treatment initiation or any dose change 1, 2, 3
- For injectable formulations, measure levels midway between injections to capture representative values, targeting 450-600 ng/dL at this timepoint 1
- After achieving stable therapeutic levels, monitor every 6-12 months 1, 2
The Endocrine Society specifically recommends re-evaluation at 3 months after testosterone initiation and at least annually thereafter 2, 3
Additional Monitoring Parameters
Beyond testosterone levels, the 2-3 month follow-up should include:
- Hematocrit/hemoglobin to screen for erythrocytosis (occurs in 43.8% with IM injections vs 15.4% with transdermal) 1
- PSA and digital rectal examination in men over 40 years 1, 7
- Assessment of symptom improvement (sexual function, energy, mood) 2, 3
Common Pitfalls to Avoid
- Do not diagnose testosterone deficiency based on a single low measurement - physiologic variation, acute illness, medications, and circadian rhythm can cause transient low values 3, 6
- Do not retest too early after starting therapy - allow 2-3 months for steady-state levels to be achieved before making dose adjustments 1, 2
- Do not measure testosterone at random times of day - always use morning measurements (8-10 AM) for consistency and accuracy 5, 3
- Do not ignore the clinical context - testosterone levels alone without symptoms do not warrant treatment 4, 3, 6