Why is growth hormone stimulation test done?
Q: I was advised to get a growth hormone stimulation test done for my 5-year-old daughter. Which are the reliable places for these tests?
A:Growth hormone (GH) is produced and released from the anterior pituitary gland under the influence of the hypothalamus. In children, it promotes and stimulates linear skeletal growth. The hormone is secreted in a pulsatile (short, concentrated secretion) and sporadic fashion and thus, a single test of the GH level is usually not performed. Testing for it is usually done to help evaluate pituitary function or if there are symptoms of growth hormone abnormalities. GH stimulation test is used to screen for hypopituitarism (i.e. low functioning) and the test helps diagnose growth hormone deficiency. IGF-1 (Insulin-like growth factor-1) is often measured during GH provocation testing and is used by itself or with GH as a monitoring tool as it mirrors GH excesses and deficiencies. Its level is stable throughout the day and hence, it is a useful indicator of average GH levels. Since GH is released by the pituitary in bursts, random GH levels are not very useful and there is too much overlap between abnormal results and normal daily variation. GH levels are higher on waking and increase with exercise and stress. There is no standard reference range for this test as the values are dependent on many factors like patient age, gender, sample population, and test method. The test results have different meanings in different labs and each lab mentions its specific reference range. It is best for you to consult your endocrinologist and go to a lab, which is experienced in this kind of testing.