Sector: Hormone 1
Test Name: Growth Hormone
Normal Range: female:up to 8
Growth hormone (GH) is produced by the pituitary, situated at the base of the brain, behind the bridge of your nose and has growth promoting properties. It is measured to check if there is under or overproduction. In addition it is used to examine the function of the pituitary and to monitor the effectiveness of treatment.
The evaluation of GH status is based on clinical findings, medical history, imaging and biochemical tests. Slow growth in height and delayed development (in children),whilst decreased bone density and/or muscle strength, and increased lipids (in adults) could all be related to insufficient GH production. Symptoms suggestive of gigantism in children or acromegaly in adults may be a result of excess GH production. It is also measured as part of an evaluation of pituitary function.
After an overnight fast, several blood samples are taken at timed intervals from veins in your arm, as part of a stimulation or suppression test. Pre-adolescents require priming prior to performing a stimulation test. A sample is usually taken for measurement of insulin-like growth factor-1 (IGF-1) on the baseline sample. When monitoring treatment for GH excess a single sample of blood may be drawn following a fast.
In healthy adults GH is released in bursts throughout the day, it rises sharply 3-4 hours after a meal and within 60 minutes after the onset of sleep making random GH results in general uninterruptable. GH may be measured after stimulation or suppression testing. Fasting levels are used to monitor treatment for GH excess.
GH is needed for a child’s normal growth and development. It promotes growth of the long bones from birth through puberty. Children with insufficient GH production grow more slowly and are small in size for their age; one of the first symptoms of growth hormone deficiency (GHD). It should be noted that short stature can also be related to familial traits or other genetic disorders. Constitutional delay (i.e. temporary delay in growth of no obvious cause) is the most common cause of short stature in childhood.
An excess of GH is most often due to a benign GH-secreting pituitary tumour i.e. a tumour that has not spread to other tissues, although larger tumours can have other effects e.g. headaches and impaired vision Gigantism is a disorder resulting from long-term secretion of too much GH, which increases the growth of muscle, bones and connective tissue in childhood or adolescence before the end of puberty. This results in a child becoming excessively tall (e.g. over 2.1 meters). Children with excessive GH production may also have thickening of their facial features, general weakness, delayed puberty, and headaches.
In adults GH plays a role in regulating bone density, muscle mass, and lipid metabolism. Deficiencies can lead to decreased bone densities, lower muscle mass, and altered lipid concentrations. Excess GH in adults can lead to acromegaly, with bone and skin thickening. Symptoms such as sweating, fatigue, headaches and joint pain can be subtle at first. Increased GH concentrations can lead to enlargement of the hands, feet, facial bones and internal organs and carpal tunnel syndrome (trapped nerves). If untreated, acromegaly in adults and gigantism in children can lead to complications such as type 2 diabetes, increased cardiovascular disease risk, high blood pressure, arthritis, and in general, a decreased life span.
GH stimulates the secretion of the true growth factors, most notably IGF-1. The concentration of which represents the secretion of GH in the previous few days. This is measured prior to stimulation or suppression tests used to diagnose GH abnormalities and to monitor treatment.
How is the sample collected for testing?
A GH suppression or stimulation tests is performed after fasting for 10 to 12 hours when a blood sample is taken from a vein in the arm. Under medical supervision, a standard glucose solution is given to the patient to drink (for a suppression test), or an intravenous (IV) injection of a solution of insulin, glucagon, arginine, clonidine or GH releasing hormone (GHRH, for a stimulation test) is given through a vein in your arm. Blood samples are then taken from your veins at timed intervals. GH is measured on each sample collected to look at the change in levels over time. Sometimes it is necessary to perform a second test.
During treatment for growth hormone excess a sample of blood may be taken, following a fast, to monitor growth hormone production.
Is any test preparation needed to ensure the quality of the sample?
Samples collected for stimulation or suppression tests are collected after fasting. Pre-adolescents are usually primed with sex steroids prior to a stimulation test.