What bloodwork is initially recommended for a patient with a suspected pituitary adenoma?

Initial Bloodwork for Suspected Pituitary Adenoma

For patients with suspected pituitary adenoma, comprehensive hormonal evaluation should be performed including prolactin, IGF-1, morning cortisol, ACTH, thyroid function tests, and gonadal hormones to assess both hypersecretion and potential hypopituitarism. 1, 2, 3

Hormonal Evaluation Algorithm

1. Screening for Hormone Hypersecretion

• Prolactin: Essential first-line test as prolactinomas are the most common functioning pituitary adenomas (32-66% of cases) 2
• IGF-1: For screening of growth hormone excess (acromegaly/gigantism)
• Morning cortisol and ACTH: For screening of Cushing's disease
• TSH and free T4: To detect thyroid-stimulating hormone-secreting tumors

2. Assessment for Hypopituitarism

• Gonadal axis:
  • Males: Total testosterone, LH, FSH
  • Females: Estradiol, LH, FSH (in context of menstrual status)
• Adrenal axis: Morning cortisol
• Thyroid axis: TSH, free T4
• Posterior pituitary function: Serum sodium, plasma osmolality (if diabetes insipidus suspected)

3. Additional Testing Based on Clinical Presentation

For Suspected Cushing's Disease

• Late-night salivary cortisol (best screening test) 2
• 24-hour urinary free cortisol
• Overnight dexamethasone suppression test

For Suspected Acromegaly

• Oral glucose tolerance test with growth hormone levels if IGF-1 is elevated 2, 3

For Suspected Prolactinoma

• Repeat prolactin measurement if initially elevated (to confirm)
• Rule out medication-induced hyperprolactinemia
• Consider serial dilutions if very high levels to avoid "hook effect" 3

Important Clinical Considerations

Timing of Imaging

• MRI with and without contrast using high-resolution pituitary protocols is the gold standard imaging after biochemical testing suggests pituitary adenoma 1
• Pre-contrast (T1 and T2) and post-contrast-enhanced (T1) thin-sliced pituitary MRI should be performed 1

Common Pitfalls to Avoid

• Don't miss hypopituitarism: Always assess for hormonal deficiencies, especially with macroadenomas, as they occur in 34-89% of patients 3
• Don't rely solely on imaging: Biochemical confirmation should precede or accompany imaging studies
• Don't overlook medication effects on prolactin: Many medications can elevate prolactin levels and mimic prolactinoma
• Don't forget to assess visual fields: Formal visual field testing is essential for tumors near the optic chiasm 3

Special Considerations

• For equivocal cases of ACTH-dependent Cushing's syndrome, inferior petrosal sinus sampling may be necessary to distinguish pituitary from ectopic sources 1, 2
• In cases of suspected hyperfunctioning pituitary adenoma with negative imaging, specialized testing like dynamic hormone stimulation tests may be required 1

By following this systematic approach to hormonal evaluation, the diagnosis of pituitary adenoma can be established efficiently, allowing for appropriate treatment planning and improved patient outcomes.