What labs should be ordered to check for pituitary or adrenal gland abnormalities?

Laboratory Tests for Evaluating Pituitary and Adrenal Gland Abnormalities

For suspected pituitary or adrenal gland abnormalities, a comprehensive panel of laboratory tests should include morning serum cortisol and ACTH, thyroid function tests (TSH, free T4), electrolytes, and appropriate sex hormones. 1

Initial Laboratory Evaluation

Core Tests for All Patients

• Morning serum cortisol and ACTH (8 AM preferred)
  • Low cortisol with high ACTH suggests primary adrenal insufficiency
  • Low cortisol with low/normal ACTH suggests secondary (pituitary) adrenal insufficiency 1, 2
• Thyroid function tests
  • TSH and free T4 to assess thyroid axis 1
• Electrolytes
  • Sodium, potassium (hyperkalemia may indicate primary adrenal insufficiency) 1, 2
• Sex hormones
  • Males: LH, FSH, testosterone
  • Females: LH, FSH, estradiol (in premenopausal women) 1

Additional First-Line Tests

• Prolactin
  • Essential to rule out prolactinoma or stalk effect 1, 3
• IGF-1
  • To screen for growth hormone excess/deficiency 1
• Metabolic panel and complete blood count
  • To assess overall metabolic status and identify anemia 1

Confirmatory Testing

For Suspected Adrenal Insufficiency

• ACTH stimulation test (Synacthen/Cosyntropin test)
  • Gold standard for diagnosing adrenal insufficiency
  • Peak serum cortisol <500 nmol/L (18 μg/dL) after 250 μg ACTH injection indicates adrenal insufficiency 1
  • For equivocal results with morning cortisol between 3-15 μg/dL 1

For Suspected Cushing's Syndrome

• 24-hour urinary free cortisol
• Late-night salivary cortisol
• Low-dose dexamethasone suppression test 1

For Suspected Hypopituitarism

• Growth hormone stimulation testing (if clinically indicated)
• DHEAS levels (often low in secondary adrenal insufficiency) 2, 4

Special Considerations

Imaging

• MRI of the brain with pituitary/sellar cuts
  • Indicated for patients with:
    • Multiple hormonal deficiencies
    • New severe headaches
    • Visual changes
    • Diabetes insipidus (which may indicate metastatic disease) 1

Timing Considerations

• Morning samples (7-9 AM) are critical for accurate assessment of cortisol and ACTH 2, 5
• Cortisol levels <250 nmol/L (9 μg/dL) with elevated ACTH during acute illness strongly suggest primary adrenal insufficiency 1
• Cortisol levels <400 nmol/L (14.5 μg/dL) with elevated ACTH during acute illness raise strong suspicion for adrenal insufficiency 1

Pitfalls to Avoid

1. Failure to test for multiple hormonal axes

   • Up to 85% of patients with non-functioning pituitary adenomas have partial hypopituitarism 1
   • Panhypopituitarism occurs in 6-29% of cases 1

2. Misinterpreting cortisol levels

   • Exogenous steroid use (including inhaled steroids) can confound interpretation 1
   • TSH may be mildly elevated (4-10 IU/L) in adrenal insufficiency due to lack of cortisol's inhibitory effect 1

3. Overlooking subclinical disease

   • Some functioning pituitary tumors may not present with classic clinical features but still show laboratory abnormalities 1, 6

4. Delaying treatment for diagnostic testing

   • Treatment of suspected acute adrenal insufficiency should never be delayed for diagnostic procedures 1

Follow-up Testing

• For patients diagnosed with adrenal insufficiency or hypopituitarism, regular monitoring of replacement therapy is essential
• For patients on glucocorticoid replacement: blood pressure, electrolytes, and glucose monitoring 2
• For patients with pituitary tumors: regular assessment of all anterior pituitary hormones 1, 6

By systematically evaluating these laboratory parameters, clinicians can effectively diagnose pituitary and adrenal abnormalities, leading to appropriate treatment and improved patient outcomes.