Unit Converter
Human growth hormone (hGH)
(Somatotropin – Key Hormone for Growth, Metabolism & GH-Related Disorders)
Synonyms
- hGH
- Growth hormone (GH)
- Somatotropin
- Pituitary growth hormone
- Recombinant GH (rhGH – for therapy, not for lab assay)
Units of Measurement
- mIU/L
- ng/mL
- ng/dL
- ng/100 mL
- ng%
- µg/mL
Key Conversions
(Molecular Weight ≈ 22,000 Da for 22-kDa GH)
1 ng/mL = 1 µg/L
1 ng/mL ≈ 22 mIU/L (assay-specific)
1 mIU/L ≈ 0.045 ng/mL
1 ng/dL = 0.01 ng/mL
ng% = ng/dL = ng/100 mL
1 µg/mL = 1000 ng/mL
⚠️ Note: Conversion between mIU/L and ng/mL varies slightly by assay manufacturer because WHO GH standards differ. The above values reflect WHO International Standard IS 98/574.
Description
Growth hormone (hGH) is a peptide hormone produced by anterior pituitary somatotrophs.
It is secreted in pulses, mainly during sleep.
Key physiological actions (mediated directly and via IGF-1):
- Stimulates linear growth in children
- Increases protein synthesis
- Enhances lipolysis
- Supports bone mineralization
- Regulates glucose homeostasis
- Promotes organ growth and repair
GH secretion is controlled by:
- GHRH (stimulates)
- Somatostatin (inhibits)
- Ghrelin (potent stimulator)
Clinical Significance
Elevated hGH
1. Acromegaly (Adults)
- Caused by GH-secreting pituitary adenoma
- Symptoms: enlarged hands/feet, coarse facial features, hypertension, diabetes, OSA
- Diagnosis: Failure of GH suppression during OGTT (GH > 1 ng/mL or >0.4 ng/mL depending on assay) + high IGF-1
2. Gigantism (Children)
GH excess before epiphyseal closure → abnormal linear growth.
3. Physiological Causes
- Exercise
- Stress
- Hypoglycemia
- Pregnancy
- Deep sleep stages
4. Starvation / Anorexia Nervosa
Low glucose/insulin → high GH + low IGF-1.
5. Untreated Diabetes Mellitus
GH secretion rises to counter metabolic stress.
Low hGH
1. Growth Hormone Deficiency (GHD)
- Congenital (pituitary hypoplasia, genetic defects)
- Acquired (tumors, surgery, radiation, trauma)
Symptoms in children:
- Short stature
- Slow growth velocity
- Delayed bone age
Symptoms in adults:
- Low muscle mass
- High fat mass
- Fatigue
- Dyslipidemia
2. Hypopituitarism
Panhypopituitarism → low GH and other pituitary hormones.
3. Chronic Illness or Under-nutrition
Functional GH deficiency pattern.
Reference Intervals
(Highly assay-dependent; values below are Mayo/ARUP averages)
Basal (Random) GH Levels - Adults
- < 5 ng/mL typical
- Fasting morning values often <1 ng/mL
Children
Random GH levels are not reliable (due to pulsatility).
Stimulated testing required.
Stimulation Test Cutoffs
(Endocrine Society GH deficiency criteria)
Children – GH Deficiency
Peak GH after stimulation (clonidine, arginine, glucagon):
- <10 ng/mL (older assays)
- <7 ng/mL (newer assays)
- <5 ng/mL (ultrasensitive assays)
Adults – GH Deficiency
Glucagon stimulation or ITT:
- <3 ng/mL (obesity adjusted)
- <1 ng/mL using ultrasensitive assays
Acromegaly Diagnosis (OGTT)
- GH NOT suppressed to <1 ng/mL (classic cutoff)
- If using ultrasensitive assay: <0.4 ng/mL
IGF-1 must be elevated to confirm diagnosis.
Diagnostic Uses
1. Growth Hormone Deficiency Testing
GH stimulation tests using:
- Insulin tolerance test (gold standard)
- Glucagon test
- Clonidine
- Arginine
- GHRH + arginine (where available)
2. Acromegaly Diagnosis & Monitoring
- GH suppression test
- IGF-1 measurement
- Post-surgical GH nadir
3. Pediatric Growth Disorders
- Short stature evaluation
- Delayed puberty workup
4. Metabolic Disorders in Adults
GH deficiency associated with:
- Dyslipidemia
- Osteopenia
- Increased fat mass
5. Critical Illness Patterns
GH resistance → high GH + low IGF-1.
Analytical Notes
- GH is pulsatile → random levels are NOT diagnostic
- Use stimulation/suppression tests for accuracy
- EDTA or serum acceptable
- GH unstable → rapid processing preferred
- Obesity lowers GH secretion (important for cutoff adjustment)
Clinical Pearls
- IGF-1 is the preferred screening test for both GH excess and deficiency.
- Random GH levels are not useful except when extremely high.
- In acromegaly, GH fails to suppress after glucose and IGF-1 is elevated.
- GH levels vary with stress, sleep, exercise—interpret cautiously.
- Pediatric cutoffs depend heavily on assay generation (older vs ultrasensitive).
Interesting Fact
GH secretion peaks during deep sleep (stage N3), explaining why sleep disturbances can impair growth in children.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Pituitary Hormones.
- Endocrine Society Clinical Practice Guideline - GH Deficiency & Acromegaly.
- Pediatric Endocrine Society - GH Testing Standards.
- Mayo Clinic Laboratories - GH Testing.
- ARUP Consult - GH Deficiency & Acromegaly Evaluation.
- NIH - Growth Hormone Physiology.