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

Initial Blood Work for Suspected Pituitary Adenoma

All patients with suspected pituitary adenoma require comprehensive anterior pituitary axis testing including prolactin, IGF-1, thyroid function, adrenal function, and gonadal hormones to assess for both hormone hypersecretion and hypopituitarism. 1

Essential Hormone Testing

Assess for Hormone Hypersecretion

• Prolactin (PRL): Mandatory in all patients to rule out prolactinoma, which may not be clinically suspected and accounts for 32-66% of pituitary adenomas 1, 2

• Insulin-like Growth Factor 1 (IGF-1): Recommended to detect clinically silent growth hormone-secreting tumors, as up to 46% of apparently nonfunctioning adenomas show GH immunostaining despite lack of clinical acromegaly 1

• 24-hour urinary free cortisol or late-night salivary cortisol: Screen for ACTH-secreting tumors causing Cushing's disease 3, 2

• TSH with free T4 and free T3: Evaluate for rare TSH-secreting adenomas (1% of cases) 3, 2

Assess for Hypopituitarism

The prevalence of hypopituitarism in pituitary adenomas is substantial, with deficiencies often exceeding clinical suspicion 1:

• Thyroid axis: TSH and free T4 to detect central hypothyroidism (present in 8-81% of patients) 1

• Adrenal axis: Morning cortisol ± ACTH (adrenal insufficiency occurs in 17-62% of patients) 1

• Gonadal axis:

  • In women: LH, FSH, estradiol
  • In men: LH, FSH, testosterone
  • Hypogonadism is one of the most commonly affected axes 1

• Growth hormone axis: While GH deficiency is common (most frequently affected axis), routine testing is complex and may be deferred to endocrinology 1

Critical Clinical Considerations

Preoperative hormone replacement is mandatory for patients with adrenal insufficiency and significant hypothyroidism before any surgical intervention. 1 The cutoff values for initiating thyroid and adrenal replacement differ in panhypopituitarism versus isolated deficiencies, making comprehensive testing essential 1.

Common Pitfalls to Avoid

• Do not assume normal function based on clinical presentation alone: Hormone deficiencies frequently exceed clinical suspicion across all pituitary axes 1

• Do not miss prolactinomas: Even modest prolactin elevations warrant attention, as dopamine agonists are first-line treatment rather than surgery 3, 2, 4

• Do not overlook "stalk effect": Mild prolactin elevation (typically <200 ng/mL) may result from stalk compression by a nonfunctioning adenoma rather than a true prolactinoma 3

• Coordinate with endocrinology early: Interpretation of pituitary hormone testing requires specialized expertise, particularly for dynamic testing that may be needed in selected cases 1, 3, 4

Additional Baseline Testing

• Electrolytes and renal function: Essential for perioperative management and to assess for diabetes insipidus (uncommon at presentation, occurring in ~7% of cases) 1

• No role for routine biomarkers or genetic testing: Unless familial syndrome suspected (particularly in children/adolescents) 1