What labs are indicated for suspected pituitary (Pituitary gland) abnormalities?

Laboratory Evaluation for Suspected Pituitary Abnormalities

All patients with suspected pituitary abnormalities require comprehensive anterior pituitary axis testing, including prolactin, IGF-1, thyroid function (TSH and free T4), adrenal function (morning cortisol and ACTH), and gonadal hormones (FSH, LH, and estradiol or testosterone), regardless of which specific deficiency is clinically suspected. 1, 2, 3

Essential Baseline Hormone Panel

The following morning hormone measurements should be obtained in all patients:

Thyroid Axis

• TSH and free T4 to detect central hypothyroidism, which presents with low free T4 and low/normal TSH (unlike primary hypothyroidism where TSH is elevated) 1, 3
• Central hypothyroidism occurs in 8-81% of patients with pituitary disorders 2, 3

Adrenal Axis

• Morning cortisol and ACTH to assess for central adrenal insufficiency, which presents with low cortisol and low/normal ACTH 1, 3
• Adrenal insufficiency occurs in 17-62% of patients with pituitary adenomas 2, 3
• Critical: If both adrenal insufficiency and hypothyroidism are present, steroids must be started before thyroid hormone replacement to avoid precipitating an adrenal crisis 3

Gonadal Axis

• FSH, LH, and estradiol (in women) or testosterone (in men) to detect hypogonadotropic hypogonadism, which presents with low sex hormones and low/normal gonadotropins 1, 3
• Hypogonadism is one of the most commonly affected axes, occurring in 36-96% of patients 1, 3

Prolactin

• Prolactin measurement is mandatory in all patients to rule out hyperprolactinemia, even when not clinically suspected 1, 2, 3
• Prolactinomas account for 32-66% of pituitary adenomas 2, 4
• Hyperprolactinemia can cause menstrual irregularities, galactorrhea, loss of libido, and infertility 1, 4

Growth Hormone Axis

• IGF-1 measurement is essential to assess for GH excess and to rule out clinically silent GH-secreting tumors 1, 2, 3
• Up to 46% of apparently nonfunctioning adenomas show GH immunostaining despite lack of clinical acromegaly 2
• The GH axis is the most commonly affected in nonfunctioning adenomas (61-100% of patients) 3

Rationale for Comprehensive Testing

The prevalence of hypopituitarism in pituitary disorders is substantial (37-85% in nonfunctioning adenomas), and panhypopituitarism occurs in 6-29% of patients, making comprehensive evaluation of all axes essential rather than selective testing. 3

The cutoff values for hormone replacement differ in isolated deficiencies versus panhypopituitarism, making it critical to identify all deficiencies present 1, 2

Dynamic Testing When Indicated

Adrenal Function

• 1 mcg cosyntropin (ACTH) stimulation test should be performed when baseline morning cortisol levels are equivocal 3
• This test must be performed before administering steroids to avoid interference with results 3

Growth Hormone Deficiency

• Patients with 3 or more pituitary hormone deficiencies are highly likely to have GH deficiency and do not require dynamic testing 3
• For isolated suspected GH deficiency, wait 6-12 months after pituitary surgery before testing, as recovery is often delayed 3

Additional Laboratory Tests

• Electrolytes and renal function are essential for perioperative management and to assess for diabetes insipidus (occurs in ~7% of cases) 2, 3
• Glucose and HbA1c should be measured as part of baseline metabolic assessment 3

Preoperative Considerations

Replacement therapy for adrenal insufficiency and significant hypothyroidism must be initiated preoperatively before any surgical intervention. 2, 3

Genetic Testing

• Genetic assessment should be offered to all children and young people with pituitary adenomas (strong recommendation, high-quality evidence) 3
• In adults, routine genetic testing is not recommended unless a familial syndrome is suspected 2

Common Pitfalls to Avoid

• Never start thyroid hormone replacement before addressing adrenal insufficiency - this can precipitate life-threatening adrenal crisis 3
• Do not rely on selective testing based on clinical suspicion alone, as hormone deficiencies often exceed clinical suspicion 2, 3
• Avoid testing for GH deficiency too early after surgery; wait at least 6-12 months for accurate assessment 3
• Remember that diabetes insipidus is uncommon in pituitary adenomas (only 7% at presentation), so posterior pituitary testing is not routinely required unless clinically indicated 3