Initial Laboratory Assessment for Pituitary Mass
All patients with a pituitary mass should undergo comprehensive endocrine evaluation of all anterior pituitary axes to assess for both hormone hypersecretion and hypopituitarism, including prolactin, IGF-1, thyroid function, adrenal function, and gonadal function. 1
Essential Laboratory Tests
Hormone Hypersecretion Screening
Prolactin (PRL): Measure in all patients regardless of symptoms, as hyperprolactinemia occurs in 25-65% of nonfunctioning adenomas due to stalk compression 1. Prolactin levels >200 ng/mL suggest prolactinoma, while levels 85-200 ng/mL may indicate stalk effect from a nonfunctioning adenoma 2.
Insulin-like Growth Factor 1 (IGF-1): Obtain in all patients to screen for clinically silent growth hormone hypersecretion, as up to 45% of presumed nonfunctioning adenomas show GH immunostaining without clinical acromegaly 1.
Morning cortisol and ACTH: Screen for Cushing's disease if clinically suspected (obesity, hypertension, diabetes, striae) 3, 4. Evening salivary cortisol is the best screening test for hypercortisolism 4.
TSH and free T4: Evaluate for TSH-secreting adenomas (rare, <1% of cases) if hyperthyroidism is present 3, 4.
Hypopituitarism Assessment
The prevalence of hypopituitarism in pituitary masses is substantial (37-85% have at least one axis deficiency), making comprehensive screening essential 1:
Thyroid axis: TSH and free T4 to detect central hypothyroidism (present in 8-81% of patients) 1. Replacement is required preoperatively if significant hypothyroidism is present 1.
Adrenal axis: Morning cortisol (8 AM) ± ACTH to assess for adrenal insufficiency (present in 17-62% of patients) 1. Cortisol <3 μg/dL indicates deficiency; >15 μg/dL excludes it. Values between 3-15 μg/dL require ACTH stimulation testing 3. Adrenal insufficiency must be replaced preoperatively to prevent perioperative crisis 1.
Gonadal axis:
Growth hormone axis: While GH deficiency is the most common deficit (61-100% of patients), routine testing is not always performed initially unless clinically indicated, as replacement is typically deferred until after surgical intervention 1.
Secondary Evaluation Based on Initial Results
If Prolactin is Elevated
- Repeat prolactin measurement to confirm elevation is not spurious 1.
- If persistently elevated >200 ng/mL, likely prolactinoma; consider dopamine agonist therapy as first-line treatment 4, 2.
- If prolactin 85-200 ng/mL with large mass, likely stalk effect from nonfunctioning adenoma 2.
If Low Testosterone with Low/Normal LH
- Measure prolactin to screen for hyperprolactinemia 1.
- If prolactin normal but testosterone <150 ng/dL, consider pituitary MRI regardless of prolactin level, as non-secreting adenomas may be present 1.
If Cushing's Disease Suspected
- Perform overnight dexamethasone suppression test or 24-hour urinary free cortisol 4.
- If confirmed, bilateral inferior petrosal sinus sampling with CRH stimulation may be needed to distinguish pituitary from ectopic ACTH source, especially if MRI is negative 2.
Critical Pitfalls to Avoid
Do not rely on symptoms alone to guide hormone testing—many hormone deficiencies and excesses are clinically silent, particularly GH excess and early hypopituitarism 1.
Do not assume normal prolactin excludes a pituitary mass—nonfunctioning adenomas are common (15-54% of all adenomas) and may have normal prolactin 4.
Always assess adrenal and thyroid function preoperatively in macroadenomas, as unrecognized deficiencies can cause perioperative complications 1.
Cutoff values for hormone replacement differ in panhypopituitarism versus isolated deficiencies, making comprehensive axis testing essential 1.