What labs should be run for a 22-year-old female-to-male (FTM) patient taking testosterone (testosterone) who presents with galactorrhea (spontaneous milk production)?

Laboratory Evaluation for Galactorrhea in a Female-to-Male Patient on Testosterone Therapy

For a patient on testosterone therapy presenting with galactorrhea, serum prolactin measurement should be the primary laboratory test, followed by luteinizing hormone (LH) and thyroid-stimulating hormone (TSH) levels to identify the underlying cause. 1

Initial Laboratory Workup

1. Serum Prolactin Level

   • Most important initial test as hyperprolactinemia is the most common cause of galactorrhea
   • If elevated, repeat to ensure the elevation is not spurious 1

2. Luteinizing Hormone (LH)

   • Essential to determine the etiology of potential testosterone-related issues
   • Helps distinguish between pituitary, hypothalamic, and medication-induced causes 1

3. Thyroid-Stimulating Hormone (TSH)

   • Hypothyroidism can cause hyperprolactinemia and galactorrhea
   • Should be included in initial evaluation 2

4. Estradiol Level

   • Important in transgender patients on testosterone as estrogen/androgen imbalance may contribute to galactorrhea
   • Testosterone therapy can aromatize to estradiol 1, 3

5. Total and Free Testosterone Levels

   • To assess adequacy of hormone therapy and potential conversion to estrogen
   • Free testosterone index (total testosterone/SHBG ratio) provides better assessment 1

6. Renal Function Tests

   • Chronic renal failure can cause hyperprolactinemia 2

Additional Testing Based on Initial Results

• If prolactin is elevated:

  • Repeat measurement to confirm
  • Consider pituitary MRI if level remains elevated and no medication cause is identified 1, 2
  • Persistently high prolactin levels can indicate pituitary tumors such as prolactinomas 1

• If LH is low or low/normal with elevated prolactin:

  • Consider pituitary MRI regardless of prolactin level if testosterone is very low (<150 ng/dL) 1
  • Non-secreting adenomas may be present 1

Important Considerations

• Medication review is crucial - Testosterone itself may contribute to galactorrhea through conversion to estradiol 3

• Timing of sample collection - Hormone levels should be measured in the morning (around 8 am) for accuracy 1

• Potential causes in this specific case:

  1. Testosterone-induced estrogen elevation through aromatization
  2. Medication-induced hyperprolactinemia (check for other medications)
  3. Pituitary microadenoma or other pituitary disorder
  4. Hypothyroidism

Management Algorithm

1. Measure prolactin, LH, TSH, estradiol, and testosterone levels
2. If prolactin is elevated:
   • Review all medications
   • Consider temporary reduction or adjustment of testosterone dose
   • If no medication cause identified, proceed to pituitary imaging
3. If prolactin is normal but galactorrhea persists:
   • Assess estradiol/testosterone ratio
   • Consider adjusting testosterone formulation or dosage

Pitfalls to Avoid

• Don't assume galactorrhea is normal in transgender patients on testosterone therapy
• Don't overlook thyroid dysfunction as a potential cause
• Don't immediately attribute symptoms to testosterone therapy without ruling out pituitary pathology
• Don't delay imaging if prolactin levels are significantly elevated or if there are other concerning symptoms like headaches or visual changes

By following this systematic approach to laboratory evaluation, you can identify the underlying cause of galactorrhea in this patient and develop an appropriate treatment plan to address both the symptom and its cause.