GH

Growth Hormone

Hormones

What is Growth Hormone?

Growth hormone (GH), also called somatotropin, is a 191-amino acid peptide hormone secreted by somatotroph cells in the anterior pituitary gland. GH is the primary hormone regulating linear growth in children and plays crucial metabolic roles throughout life, including stimulating protein synthesis, promoting lipolysis (fat breakdown), opposing insulin action on glucose metabolism, and maintaining muscle and bone mass. GH acts both directly on tissues and indirectly through stimulating the liver and other tissues to produce insulin-like growth factor 1 (IGF-1).

GH secretion is pulsatile, with the largest bursts occurring during deep sleep (stages 3 and 4). This pulsatile pattern means random GH measurements are unreliable for diagnosis—levels can be undetectable between pulses even in healthy individuals. GH secretion is regulated by two hypothalamic hormones: growth hormone-releasing hormone (GHRH, stimulatory) and somatostatin (inhibitory). Factors that stimulate GH release include sleep, exercise, fasting, hypoglycemia, and certain amino acids, while obesity, hyperglycemia, and elevated IGF-1 suppress it.

Why It Matters

Growth hormone excess (acromegaly in adults, gigantism in children) causes progressive disfigurement, metabolic complications, cardiovascular disease, and increased mortality if untreated. GH deficiency in children causes short stature and delayed development, while adult GH deficiency leads to increased body fat, decreased muscle mass, reduced bone density, impaired quality of life, and adverse cardiovascular risk profiles. Early diagnosis of both excess and deficiency significantly improves outcomes. GH is also relevant in sports medicine as a banned performance-enhancing substance.

Normal Reference Ranges

GroupRangeUnit
Adult Men (random)0.01–0.97ng/mL
Adult Women (random)0.01–3.61ng/mL
GH Suppression Test (post-glucose)<0.3ng/mL (excludes acromegaly)
GH Stimulation Test (peak)>5–10ng/mL (excludes deficiency)

Reference ranges may vary by laboratory. Always compare results to the ranges provided by your testing facility.

What High GH Levels Mean

Common Causes

  • Pituitary adenoma producing GH (acromegaly/gigantism)
  • Ectopic GHRH secretion (rare—carcinoid, pancreatic tumors)
  • Exercise, stress, or fasting (physiological)
  • Deep sleep sampling
  • Uncontrolled diabetes mellitus
  • Malnutrition or anorexia nervosa

Possible Symptoms

  • Enlargement of hands, feet, and jaw (acromegaly)
  • Coarsening of facial features
  • Excessive sweating and oily skin
  • Joint pain and arthritis
  • Carpal tunnel syndrome
  • Sleep apnea
  • Headaches and visual field defects (from pituitary mass)
  • Hypertension and cardiomegaly

What to do: Suspected acromegaly is screened with IGF-1 (which reflects integrated GH secretion and does not fluctuate). If IGF-1 is elevated, an oral glucose tolerance test (OGTT) with GH measurement is the confirmatory test—in healthy individuals, glucose suppresses GH to <0.3 ng/mL, but in acromegaly GH fails to suppress. Pituitary MRI identifies the adenoma. First-line treatment is transsphenoidal surgery. Medical therapy with somatostatin analogs (octreotide, lanreotide), GH receptor antagonists (pegvisomant), or dopamine agonists (cabergoline) is used when surgery is not curative or feasible. Radiation therapy is reserved for refractory cases.

What Low GH Levels Mean

Common Causes

  • GH deficiency (congenital or acquired pituitary disease)
  • Pituitary surgery, radiation, or traumatic brain injury
  • Pituitary tumors compressing somatotrophs
  • Craniopharyngioma or other sellar/suprasellar lesions
  • Obesity (functional suppression of GH)
  • Aging (physiological decline in GH pulsatility)

Possible Symptoms

  • Short stature and growth failure in children
  • Increased body fat, especially central/abdominal
  • Decreased muscle mass and strength
  • Reduced bone density
  • Fatigue and reduced exercise capacity
  • Impaired quality of life and depressed mood
  • Elevated LDL cholesterol

What to do: GH deficiency cannot be diagnosed by a single random GH level due to normal pulsatile secretion. Provocative stimulation testing is required: insulin tolerance test (ITT) is the gold standard, where insulin-induced hypoglycemia should stimulate GH release above 5 ng/mL in adults. Alternative tests include glucagon stimulation, GHRH-arginine, and macimorelin (an oral GH secretagogue). IGF-1 below the age-appropriate range supports the diagnosis. In children, GH replacement promotes linear growth and should be started early. In adults, GH replacement (daily injections or newer long-acting formulations) improves body composition, bone density, lipid profiles, and quality of life.

When Is GH Testing Recommended?

  • When a child shows growth failure or significantly short stature
  • When physical signs of acromegaly are present (enlarged features, large hands/feet)
  • When a pituitary mass is identified on imaging
  • When evaluating pituitary function after surgery, radiation, or traumatic brain injury

Frequently Asked Questions

GH is secreted in pulses, primarily during sleep, with levels fluctuating from undetectable (<0.1 ng/mL) to peaks of 10–20 ng/mL throughout a 24-hour period. A random blood draw could catch a pulse or miss it entirely, making a single value uninterpretable. For this reason, dynamic testing is used: stimulation tests (insulin tolerance test, glucagon test) provoke GH release to see if the pituitary can respond, while suppression tests (oral glucose tolerance test) check whether GH appropriately suppresses. IGF-1, which reflects average GH activity over time, serves as a useful screening test for both excess and deficiency.
Both conditions are caused by excess GH, typically from a pituitary adenoma, but they differ based on when the excess begins. Gigantism occurs when GH excess starts before the growth plates (epiphyses) have closed in childhood or adolescence, resulting in excessive linear growth and very tall stature. Acromegaly occurs when GH excess develops after growth plate closure in adulthood—since bones can no longer grow longer, they grow wider, leading to the characteristic enlargement of hands, feet, jaw, and facial features. Both conditions share metabolic complications including insulin resistance, hypertension, sleep apnea, and cardiovascular disease.
Yes, GH secretion declines with age—a phenomenon sometimes called "somatopause." GH pulse amplitude decreases, IGF-1 levels fall, and body composition shifts toward more fat and less muscle. However, this is considered a normal physiological process, and routine GH replacement in healthy older adults is not recommended. Clinical trials of GH in elderly individuals have shown modest increases in lean mass and decreases in fat mass but also significant side effects including joint pain, edema, carpal tunnel syndrome, glucose intolerance, and potentially increased cancer risk. GH replacement is only indicated for adults with documented GH deficiency from pituitary disease, not for age-related decline.

Related Biomarkers

IGF-1Insulin-Like Growth Factor 1GLUGlucoseInsulinInsulinTSHThyroid-Stimulating Hormone

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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Reference ranges may vary between laboratories. Always consult your healthcare provider for interpretation of your specific test results.

Disclaimer: SymptomGPT is not a medical diagnosis tool and does not provide medical advice. Always consult a qualified healthcare professional. If you are experiencing a medical emergency, call 911 immediately.