growth hormone (GH) stimulation test

Indications: - evaluation of growth hormone deficiency Contraindications: 1) Caution with arginine stimulation a) severe liver disease b) severe renal disease c) acidosis 2) contraindications with glucagon & propranolol stimulation a) heart disease b) bronchial asthma c) diabetes mellitus 3) insulin stimulation - AVOID if adrenal insufficiency is suspected; may precipitate adrenal crisis Normal range: - 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) Procedure: 1) arginine stimulation: a) arginine infusion: 0.5 g/kg IV over 30 minutes b) baseline, 30, 60 & 90 minute serum growth hormone c) release of GH is stimulated in males by pretreatment with diethylstilbestrol 2.5 mg BID for 2 days d) advantage of test is absence of significant side effects e) subnormal response should be confirmed by another method (20% of normal individuals will NOT respond to arginine) 2) glucagon & propranolol stimulation: a) fast after midnight b) propranolol 0.75 mg/kg PO @ 0700 h c) glucagon 0.03 mg/kg IM @ 0900 h d) serum growth hormone baseline (before glucagon), 1100 h & 1200 h e) glucagon is NOT a potent stimulus; propranolol augments the response 3) insulin stimulation a) regular insulin 0.1-0.15 U/kg IV (child use 0.05 U/kg) b) serum growth hormone baseline (fasting), 30, 60 & 90 minutes c) also serum glucose & cortisol 1] serum glucose should fall < 50% of baseline (< 40 mg/mL) 2] serum cortisol a] should rise > 7 ug/dL above baseline b] peak response > 20 ug/dL d) observe for signs of hypoglycemia e) decreased response may result from 1] anterior pituitary dysfunction a] growth hormone deficiency b] ACTH deficiency 2] cyproheptadine, methysergide, phentolamine f) propranolol increases response g) a subnormal response should be confirmed by another method (20% of normal individuals will NOT respond to insulin) 4) L-dopa stimulation a) L-dopa: 500 mg orally (children 10 mg/kg) (preferably fasting) b) serum growth hormone baseline, 30, 60, 90 & 120 minutes after L-dopa c) factors contributing to a decreased response: 1] release inhibited by phenothiazines & TRH 2] hypopituitarism 3] hyperglycemia (serum glucose > 120 mg/dL) d) vertigo & nausea may occur in 1st 30 minutes e) a paradoxical fall in GH may occur in acromegaly f) 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 Specimen: - serum, fasting

Related

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

References

Clinical Guide to Laboratory Tests, 3rd ed. Teitz ed., W.B. Saunders, 1995