What are the initial lab tests for a woman undergoing evaluation for pituitary function?

Initial Laboratory Tests for Pituitary Function Evaluation in Women

For women undergoing evaluation of pituitary function, a comprehensive panel of hormone tests should include assessment of all anterior pituitary axes, prolactin levels, and appropriate imaging studies.

Core Laboratory Tests for Initial Evaluation

• Morning hormone measurements (preferably around 8 am):
  • Thyroid function: TSH and free T4 (to assess thyroid axis) 1
  • Adrenal function: ACTH and cortisol (to assess adrenal axis) 1
  • Gonadal function: FSH, LH, estradiol (to assess reproductive axis) 1
  • Prolactin (to rule out hyperprolactinemia) 1, 2
  • IGF-1 (to assess growth hormone axis and rule out GH hypersecretion) 1

Rationale for Comprehensive Testing

• The prevalence of hypopituitarism in patients with pituitary disorders is high, with GH deficiency and hypogonadism being most common (36-96%), followed by adrenal insufficiency (17-62%) and hypothyroidism (8-81%) 1
• Routine testing of all anterior pituitary hormones is recommended even when only specific deficiencies are clinically suspected, as the cutoff values for hormone replacement may differ in isolated deficiencies versus panhypopituitarism 1
• Prolactin testing is essential as hyperprolactinemia can cause menstrual irregularities and may indicate a prolactinoma that might not be clinically suspected 1, 2

Additional Tests Based on Clinical Presentation

• For menstrual irregularities:

  • Document menstrual pattern using a menstrual chart for at least 6 months 1
  • Consider pelvic ultrasonography if clinical features or hormonal tests suggest ovarian pathology 1

• For suspected adrenal insufficiency:

  • Consider dynamic testing with 1 mcg ACTH stimulation test or insulin tolerance test (ITT) 1, 3
  • Replacement for adrenal insufficiency should be initiated before thyroid hormone replacement if both deficiencies are present 1

• For suspected diabetes insipidus:

  • Water deprivation test (uncommon finding, reported in only 7% of patients with non-functioning pituitary adenomas) 1

Imaging Studies

• MRI of the sella with high-resolution pituitary protocol is the gold standard for imaging the pituitary gland 1, 4
  • Should include both pre-contrast (T1 and T2) and post-contrast-enhanced (T1) thin-sliced sequences 1, 4
  • Dynamic contrast-enhanced imaging may increase sensitivity for microadenoma detection 1

Common Pitfalls to Avoid

• Timing of blood sampling: Hormone measurements should be taken in the morning while resting to ensure accurate assessment 2
• Medication effects: Many drugs can cause hyperprolactinemia and should be ruled out before attributing findings to pituitary pathology 2
• Isolated testing: Evaluating only one hormone axis may miss clinically significant deficiencies in other axes 1
• Hook effect: Be aware of the "high-dose hook effect" which can cause falsely low prolactin readings in cases of large prolactinomas 2

Special Considerations

• For suspected hyperprolactinemia, confirm that samples were taken in the morning while resting 2
• In patients with suspected non-functioning pituitary adenomas, IGF-1 evaluation is recommended to rule out clinically silent GH-secreting tumors 1
• Replacement for adrenal insufficiency and significant hypothyroidism should be initiated preoperatively if surgery is planned 1

By following this systematic approach to laboratory testing, clinicians can comprehensively evaluate pituitary function in women and identify both obvious and subtle hormonal abnormalities that may impact morbidity, mortality, and quality of life.