What labs are required for initial evaluation and monitoring of patients undergoing testosterone replacement therapy?

Laboratory Tests for Testosterone Replacement Therapy

Initial laboratory evaluation for testosterone replacement therapy requires two early morning total testosterone measurements below 300 ng/dL, along with luteinizing hormone (LH), hemoglobin/hematocrit, and prolactin levels if LH is low. 1

Initial Diagnostic Evaluation

Required Laboratory Tests

• Total testosterone: Must be measured twice on separate occasions
  • Both measurements must be conducted in early morning
  • Both measurements must be below 300 ng/dL
  • Preferably using the same laboratory with the same method/instrumentation 1
• Luteinizing hormone (LH): Essential to determine the etiology of testosterone deficiency 1
• Prolactin: Required if testosterone is low with low/normal LH levels 1
• Hemoglobin/hematocrit: Must be measured before starting therapy to establish baseline 1

Additional Tests Based on Clinical Presentation

• Follicle-stimulating hormone (FSH): Required for men interested in fertility 1
• Estradiol: Measure in patients with breast symptoms or gynecomastia 1
• Cardiovascular risk assessment: Evaluate for modifiable risk factors (dyslipidemia, hypertension, diabetes, smoking) 1

Monitoring During Therapy

• Total testosterone: Check 3-6 months after starting therapy and annually thereafter
• Hemoglobin/hematocrit: Monitor periodically to detect polycythemia 2
  • If hematocrit exceeds 50%, consider withholding therapy
• Prostate-specific antigen (PSA): Monitor in men over 40 years
• Liver function tests: Particularly important with oral formulations

Special Considerations

For Patients with Severe Testosterone Deficiency

• If total testosterone is <150 ng/dL with low/normal LH, consider pituitary MRI regardless of prolactin levels 1
• Persistently elevated prolactin requires endocrinology referral 1

For Fertility Concerns

• Measure FSH and perform testicular examination 1
• Consider semen analysis if FSH is elevated 1
• Testosterone therapy suppresses spermatogenesis and can cause oligospermia 2

For Patients on Anticoagulants

• Monitor anticoagulation therapy closely as testosterone may increase sensitivity to oral anticoagulants 2

For Diabetic Patients

• Monitor blood glucose levels as testosterone may decrease blood glucose and insulin requirements 2

Common Pitfalls to Avoid

1. Inadequate diagnosis: Relying on a single testosterone measurement or not measuring in the morning
2. Missing secondary causes: Failing to measure LH and prolactin
3. Overlooking contraindications: Not screening for prostate cancer, severe lower urinary tract symptoms, or polycythemia
4. Insufficient monitoring: Not checking testosterone levels after starting therapy
5. Ignoring fertility concerns: Not discussing potential impact on fertility before starting therapy

By following this structured approach to laboratory testing for testosterone replacement therapy, clinicians can ensure proper diagnosis, appropriate treatment selection, and adequate monitoring to optimize outcomes while minimizing risks.