Laboratory Tests to Evaluate Pituitary Function
All patients with suspected pituitary disease require comprehensive endocrine evaluation of all anterior pituitary axes through basal hormone measurements, with selective use of dynamic testing for specific axes that cannot be adequately assessed by baseline values alone. 1
Essential Baseline Laboratory Tests
Mandatory Initial Panel
Prolactin (PRL): Measure in all patients with suspected pituitary pathology to rule out hypersecretion that may not be clinically apparent 1. A single measurement at any time of day is sufficient 1.
Thyroid axis: Measure TSH and free T4 to assess for hypothyroidism 1, 2. Basal levels usually suffice for evaluation of the thyrotropic axis 2.
Adrenal axis: Measure morning (8 AM) cortisol level 1. Basal cortisol may be helpful, but provocative testing is often necessary for precise characterization of adrenal insufficiency 2.
Gonadal axis:
Growth hormone (GH) axis: Measure IGF-1 (insulin-like growth factor 1) to screen for both GH excess and deficiency 1. Use age-specific and sex-specific reference ranges 1.
Dynamic Testing Requirements
When Basal Testing Is Insufficient
GH deficiency evaluation: Provocative testing is required since basal GH levels are unreliable 2. The insulin tolerance test (ITT) remains the gold standard, though GHRH-arginine test with BMI-normed reference ranges is well established as an alternative 2.
Adrenal insufficiency confirmation: If basal morning cortisol is equivocal (typically between 3-15 μg/dL), perform stimulation testing 1, 2. Options include ITT (gold standard), low-dose ACTH stimulation test, or glucagon stimulation test 3.
GH excess evaluation: If IGF-1 is elevated, perform oral glucose tolerance test (OGTT) with GH measurements 1. In adults, GH should suppress below 1 μg/L; failure to suppress suggests GH excess, though interpretation in adolescents requires consideration of pubertal stage 1.
Critical Considerations for Specific Scenarios
Nonfunctioning Pituitary Adenomas (NFPAs)
Comprehensive anterior pituitary assessment is mandatory because the prevalence of hypopituitarism is high (GH deficiency and hypogonadism most common, followed by adrenal insufficiency and hypothyroidism) 1.
Always measure prolactin even in presumed NFPAs to exclude prolactinomas that lack clinical features 1.
Measure IGF-1 to rule out clinically silent GH-secreting tumors, as up to 45.9% of NFPAs show GH immunostaining despite lack of acromegaly symptoms 1.
Hyperprolactinemia Workup
If prolactin is modestly elevated (up to 5 times upper limit of normal), repeat measurements on a different day using an indwelling cannula with 2-3 samples at 20-60 minute intervals to exclude stress-related elevation 1.
Use age-specific and sex-specific reference ranges, particularly in children and adolescents 1.
Hormone Excess Syndromes
For suspected acromegaly/gigantism: Assess all other anterior pituitary hormones for both hypofunction (mass effect) and hyperfunction (co-secretion), as 65% have hyperprolactinemia and 25-35% have other hormone deficiencies 1.
Screen for genetic syndromes: Consider testing for MEN1, Carney complex, McCune-Albright syndrome in appropriate clinical contexts 1.
Common Pitfalls to Avoid
Do not rely on combined pituitary function tests as a routine approach; stepwise evaluation based on clinical presentation is preferred 2.
Do not overlook preoperative hormone replacement: Patients with confirmed adrenal insufficiency and significant hypothyroidism require replacement before surgery 1.
Do not assume normal function without testing: Hypopituitarism rates are high in pituitary adenomas, often exceeding clinical suspicion 1.
Do not use adult cut-offs in adolescents: GH suppression testing and IGF-1 interpretation require pubertal stage-specific and sex-specific reference ranges 1.