When are pituitary function tests recommended?

Pituitary Function Tests: Recommendations and Indications

Routine endocrine evaluation of all anterior pituitary axes is recommended for patients with suspected pituitary disorders, particularly those with nonfunctioning pituitary adenomas (NFPAs), due to the high prevalence of hypopituitarism in these patients. 1

General Indications for Pituitary Function Testing

• Pituitary function tests are recommended for patients with suspected or confirmed pituitary adenomas to assess for hypopituitarism, which affects 37-85% of patients with NFPAs 1
• Complete evaluation of all anterior pituitary hormone axes is necessary as panhypopituitarism occurs in 6-29% of patients with pituitary disorders 1, 2
• Testing is indicated when clinical features suggest pituitary hormone excess (e.g., acromegaly, Cushing's disease, hyperprolactinemia) or deficiency 3
• Patients with macroadenomas almost invariably have pituitary hormone deficiencies, with GH and FSH/LH being most commonly affected, followed by TSH and ACTH 4

Specific Testing Recommendations

For Nonfunctioning Pituitary Adenomas (NFPAs)

• Routine evaluation of all anterior pituitary axes is recommended to assess for hypopituitarism (level II recommendation) 1
• Routine prolactin testing is recommended in all patients with suspected NFPA to rule out hypersecretion that might not be clinically suspected (level II recommendation) 1
• Routine insulin-like growth factor 1 (IGF-1) evaluation is recommended in all patients with suspected NFPA to rule out growth hormone hypersecretion (level III recommendation) 1

For Children and Adolescents

• Genetic assessment should be offered to all children and young people with pituitary adenomas to inform management and family surveillance (strong recommendation, high-quality evidence) 1
• Genetic testing should be offered to all children and young people with growth hormone and prolactin excess due to high prevalence of genetic abnormalities in these tumors (strong recommendation, high-quality evidence) 1

Specific Tests to Consider

• Adrenal axis: Morning cortisol, ACTH levels, and stimulation tests (e.g., overnight metyrapone test) 3, 4
• Thyroid axis: Free T4, TSH, and TRH stimulation test in selected cases 3, 5
• Gonadal axis: FSH, LH, estradiol/testosterone, and LHRH stimulation test in selected cases 3, 4
• Growth hormone axis: IGF-1 levels and GH stimulation tests 3, 5
• Prolactin: Baseline prolactin levels 1, 3

Timing of Tests

• For assessment of GH deficiency after pituitary surgery, wait at least 6-12 months after surgery before testing, as HPA axis recovery is often delayed 1
• In children with Cushing's disease, evaluate for GH deficiency 3-6 months after surgery 1

Clinical Pearls and Pitfalls

• The most commonly affected pituitary axis in NFPAs is the GH axis (61-100% of patients), followed by gonadal axis (36-96%), adrenal axis (17-62%), and thyroid axis (8-81%) 1
• Patients with 3 or more pituitary hormone deficiencies are more likely to have GH deficiency and do not need dynamic testing 1
• Laboratory tests for growth and thyroid dysfunction are among the most problematic from a methodological perspective, creating diagnostic challenges for patients in the "grey zone" of diagnosis 5
• Diabetes insipidus is uncommon in NFPAs, reported in only 7% of patients at presentation 1
• Replacement for adrenal insufficiency and significant hypothyroidism is recommended in all patients preoperatively (level II recommendation) 1

Diagnostic Algorithm

1. Initial evaluation: Complete assessment of all anterior pituitary axes with baseline hormone measurements 1, 2
2. Dynamic testing: Perform stimulation tests as needed based on clinical suspicion and baseline results 3, 4
3. Imaging: MRI of the sella with pituitary cuts for all patients with suspected pituitary disorders 2
4. Treatment prioritization: Address adrenal insufficiency first before treating other hormonal deficiencies to avoid precipitating an adrenal crisis 2
5. Follow-up: Regular monitoring of hormone replacement adequacy is necessary 2, 6