GROWTH HORMONE ( GH )

Interpretation :

• GROWTH HORMONE, SERUM-Human growth hormone (hGH, somatotropin) is a polypeptide originating in the anterior pituitary. It is 191 amino acids in length and has a molecular mass of approximately 22,000 daltons. Its metabolic effects are primarily anabolic. It promotes protein conservation and engages a wide range of mechanisms for protein synthesis. It also enhances glucose transport and facilitates the buildup of glycogen stores.

• Measurement of hGH is primarily of interest in the diagnosis and treatment of various forms of inappropriate growth hormone secretion. Clinical disorders of hyposecretion include dwarfism and unattained growth potential. Hypersecretion is associated with gigantism and acromegaly.

• Caution must be exercised in the clinical interpretation of growth hormone levels. These vary throughout the day, making it difficult to define a reference range or to judge an individual''''s status based on single determinations. Many factors are known to influence the rate of growth hormone secretion, including periods of sleep and wakefulness, exercise, stress, hypoglycemia, estrogens, corticosteroids, L-dopa, and others.

• Growth hormone-deficient individuals have fasting/resting levels similar to those found in healthy individuals. Various challenge tests have therefore been devised to differentiate these groups. Thus with the onset of deep sleep or after 15 to 20 minutes of vigorous exercise, growth hormone levels normally show a rise. Other tests of growth hormone responsiveness are based on the administration of L-dopa, arginine and insulin. Propanolol and estrogen are sometimes given in conjunction with the primary stimulus to accentuate the response.

• A small number of cases of dwarfism have been documented in which both the basal level and the response to challenge testing were normal. Such cases may involve tissue insensitivity to either growth hormone or somatomedins, or the presence of antibodies or immunoreactive but biologically inactive growth hormone.

• REFERENCE RANGE FOR GROWTH HORMONE STIMULATION TEST. Post- stimulation normal peak levels of GH are 10 ng/mL or more. In children, GH levels 7.0 ng/mL or less and in adults GH levels of 5.0 ng/mL or less indicate GH deficiency. GH levels between normal and deficient states are considered as Indeterminate.