GROWTH HORMONE, TIMED, 120 MINUTES
- GROWTH HORMONE, TIMED, 120 MINUTES
- Start Date
- Expiration Date
- CPT Codes
- Reference Test
- Transport Info
Centrifuge and immediately transfer serum to separate plastic tube
- Fasting Required?
- Patient Instructions
Fasting at least 12 hours
- Reference Range
A GH level of < or = 7 ng/mL on two or more stimulation tests is supportive of impaired GH secretion. A GH level of > 10 ng/mL with a normal IGF-1 excludes the diagnosis of GH deficiency.
In response to a glucose suppression test, a response of falling to < 2 ng/mL is shown in normal individuals. Patients with acromegaly fail to show this suppression and at times show a paradoxical increase in GH levels.
Chemiluminescent Immunometric Assay
Human growth hormone (HGH; somatotropin) is a 22,000 Dalton (22k) molecular weight polypeptide hormone secreted by the anterior pituitary. An HGH variant of 20,000 Dalton molecular weight is also present in serum. The 22k HGH is the predominant part of the total HGH in serum.
Growth hormone-releasing hormone specifically stimulates the synthesis and release of HGH by somatotropic cells of the anterior pituitary gland. Human growth hormone stimulates the liver to produce somatomedins, a group of hormones that directly promote growth. HGH indirectly affects many metabolic processes via the somatomedins including cellular uptake of amino acids and release of fatty acids from tissue stores.
There are many stimulatory and inhibitory factors for secretion of HGH. Inhibitory factors include glucose, cortisol, free fatty acids and somatostatin. Stimulatory factors include exercise, hypoglycemia, arginine, L-dopa, glucagon, histamine, vasopressin, catacholamine, slow wave sleep and stress. The measurement of serum HGH has been used in diagnosing hyposomatotropism and hypersomatotropism. The clinical disorders of hyposomatotropism include dwarfism and unattained growth potential. The clinical disorders of hypersomatotropism include gigantism in children and acromegaly in adults. Acromegaly is usually caused by pituitary adenomas and rarely caused by pancreatic tumors.
A single measurement of HGH is usually of limited clinical value because HGH secretion is pulsatile. To assess the clinical status of HIGH disorders, provocative or suppressive stimuli have been used. Provocative stimuli for an increase in serum HGH levels include exercise, sleep, insulin, clonidine, arginine, L-dopa and glucagon. For suppression of serum HGH levels, a standard glucose tolerance test is usually used. If hyposomatotropism is suspected a provocative test is used. If hypersomatotropism is suspected a glucose tolerance test is used. Blood samples can be taken before the stimulus and 0, 30, 60, 90 and 120 minutes after the stimulus.