Growth hormone

Synonym

Tubes

Additional information

Fasting and limited physical activity for 10-12 hours before the test
Make sure the patient is relaxed and recumbent for 30 minutes before the test
Handle sample gently to prevent hemolysis
Reject lipemic samples
Specimen must be refrigerated after collection as it is unstable at room temperature
Send the sample to lab immediately

Info

Growth hormone (GH) testing is a quantitative analysis of growth hormone levels in the blood
GH is a polypeptide of 191 amino acids synthesized and secreted by somatotrophs/acidophils of the anterior pituitary gland
Production of GH is controlled by many hormones and factors, which include:

Growth hormone releasing hormone stimulates both synthesis and secretion of GH
Somatostatin inhibits GH secretion
Ghrelin (a preprohormone synthesized in the fundus of the stomach) stimulates secretion of GH
Other factors such as stress, exercise, nutrition, sleep, hypoglycemia, glucagon, insulin, and vasopressin stimulate secretion of GH

The function of GH and its effects in both elevated and diminished levels are listed in the Clinical section

Clinical

Aids in the diagnosis of dwarfism or growth retardation which can result from pituitary or thyroid hypofunction
Confirm diagnosis of gigantism in children
Confirm diagnosis of acromegaly in adults
Aids in the diagnosis of pituitary and hypothalamic tumors
Evaluation and monitoring of the effecacy of GH therapy following surgery, chemotherapy, and/or radiotherapy for pituitary tumor

GH affects many body tissues directly (binding to receptors on target cells such as adipocytes) and indirectly (via insulin like growth factor-1/IGF-1)
The effects of GH include:

Increases height by stimulating multiplication and division of chondrocytes of cartilage and osteocytes, promoting growth
Increases calcium retention, with bone strengthening and increased mineralization
Increases muscle mass by stimulating new muscle cells growth
Enhances utilization of fat by stimulating triglyceride breakdown and oxidation in adipocytes
Stimulates protein anabolism in many tissues, reflected by increased amino acid uptake, increased protein synthesis, and decreased oxidation of proteins
Suppresses the ability of insulin to stimulate uptake of glucose in peripheral tissues and enhance glucose synthesis in the liver
Contributes in the maintenance and function of pancreatic islet cells
Plays a role in fuel homeostasis
Stimulates immune system functioning

GH assay as part of a stimulation test (with arginine, glucagon, insulin, or L-dopa) or a suppression test (with glucose) may yield additional information
GH deficiency may manifest clinically depending on the severity (total or partial deficiency):

Usually are 2 standard deviations below the mean for height
Growth velocity is below the 10-25th percentile, which reflects growth deceleration
Increased subcutaneous fat, especially around the trunk
The face is immature, prominent forehead, and depressed midfacial development
Dentition is delayed
Delayed onset of puberty

Cool hands & feet
Depression
Labile mood
Poor venous access
Reduced exercise tolerance
Reduced lean body mass and increased weight, with body fat mass predominantly in the abdominal region
Reduced muscle mass and strength
Thin dry skin

Excess GH may clinically manifest depending on the age group it affects and may present with:

Additional information

Nl Result

Consult your laboratory for their normal ranges as these may vary somewhat from the ones listed below.

High Result

Conditions associated with elevated GH include:

Low Result

Conditions associated with decreased GH include:

Defective pituitary development leading to pituitary aplasia
Empty sella syndrome
Encepalocele
Midline brain defects
Panhypopituitarism
Septo-optic dysplasia
Genetic abnormalities, including autosomal-recessive, autosomal-dominant, or X-linked defects or a mutation or deletion in the growth hormone gene or in growth hormone-releasing hormone

Cranial irradiation
Hypoxic insult
Infiltrative diseases including sarcoidosis, tuberculosis, histiocytosis X, hemochromatosis, and lymphocytic hypophysitis
Sheehan syndrome
Trauma
Tumors of the hypothalamic-pituitary region as in Craniopharyngioma or metastases to the pituitary (especially breast cancer)

References

Ahn CW et al. Effects of growth hormone on insulin resistance and atherosclerotic risk factors in obese type 2 diabetic patients with poor glycaemic control. Clin Endocrinol (Oxf). 2006 Apr;64(4):444-9.
eMedicine from WebMD®. Acromegaly. [Homepage on the Internet] ©1996-2007. Last updated on June 12, 2007. Last accessed on July 24, 2007. Available at URL: http://www.emedicine.com/derm/topic593.htm
eMedicine from WebMD®. Growth Hormone Deficiency. [Homepage on the Internet] ©1996-2007. Last updated on May 12, 2006. Last accessed on July 24, 2007. Available at URL: http://www.emedicine.com/med/topic930.htm
LabTestsOnline®. Growth Hormone. [Homepage on the Internet]© 2001-2007. Last reviewed on May 30, 2005. Last accessed on July 24, 2007. Available at URL: http://www.labtestsonline.org/understanding/analytes/growth_hormone/test.html
Spadoni E et al. Smith-Magenis syndrome and growth hormone deficiency. Eur j Pediatr. 2004 Jul;163(7):353-8. Epub 2004 May 8.
UTMB Laboratory Survival Guide®. HUMAN GROWTH HORMONE, serum. [Homepage on the Internet]© 2007. Last reviewed in February, 2006. Last accessed on July 24, 2007. Available at URL: http://www.utmb.edu/lsg/LabSurvivalGuide/chem/HUMAN_GROWTH_HORMONE.html