growth hormone (GH) stimulation test

Indications

• evaluation of growth hormone deficiency

Contraindications

• Caution with arginine stimulation
  • severe liver disease
  • severe renal disease
  • acidosis
• contraindications with glucagon & propranolol stimulation
  • heart disease
  • bronchial asthma
  • diabetes mellitus
• insulin stimulation
  • AVOID if adrenal insufficiency is suspected; may precipitate adrenal crisis

Reference interval

• baseline serum growth hormone: < 5 ng/mL
• rise above baseline > 5 ng/mL
• peak response > 10 ng/mL
  • @ 90 minutes with dopamine stimulation

Decreases

• diminished response: hypopituitarism (with GH deficiency)

Specimen

• serum, fasting

Procedure

• arginine stimulation:
  • arginine infusion: 0.5 g/kg IV over 30 minutes
  • baseline, 30, 60 & 90 minute serum growth hormone
  • release of GH is stimulated in males by pretreatment with diethylstilbestrol 2.5 mg BID for 2 days
  • advantage of test is absence of significant side effects
  • subnormal response should be confirmed by another method (20% of normal individuals will NOT respond to arginine)
• glucagon & propranolol stimulation:
  • fast after midnight
  • propranolol 0.75 mg/kg PO @ 0700 h
  • glucagon 0.03 mg/kg IM @ 0900 h
  • serum growth hormone baseline (before glucagon), 1100 h & 1200 h
  • glucagon is NOT a potent stimulus; propranolol augments the response
• insulin stimulation
  • regular insulin 0.1-0.15 U/kg IV (child use 0.05 U/kg)
  • serum growth hormone baseline (fasting), 30, 60 & 90 minutes
  • also serum glucose & cortisol
    • serum glucose should fall < 50% of baseline (< 40 mg/mL)
    • serum cortisol
      • should rise > 7 ug/dL above baseline
      • peak response > 20 ug/dL
  • observe for signs of hypoglycemia
  • decreased response may result from
    • anterior pituitary dysfunction
      • growth hormone deficiency
      • ACTH deficiency
    • cyproheptadine, methysergide, phentolamine
  • propranolol increases response
  • a subnormal response should be confirmed by another method (20% of normal individuals will NOT respond to insulin)
• L-dopa stimulation
  • L-dopa: 500 mg orally (children 10 mg/kg) (preferably fasting)
  • serum growth hormone baseline, 30, 60, 90 & 120 minutes after L-dopa
  • factors contributing to a decreased response:
    • release inhibited by phenothiazines & TRH
    • hypopituitarism
    • hyperglycemia (serum glucose > 120 mg/dL)
  • vertigo & nausea may occur in 1st 30 minutes
  • a paradoxical fall in GH may occur in acromegaly
  • tolerance to L-dopa may be improved by giving L-dopa 250 mg PO TID with meals for 2 days prior to the test & by giving the test dose 500 mg with food

More general terms

• special chemistry test

Additional terms

• growth hormone (GH) suppression test; glucose challenge test for acromegaly
• growth hormone (somatotropin) in serum