IGF-1 is a hormone that, along with growth hormone, helps promote normal bone and tissue growth and development. An IGF-1 test is often ordered along with GH. IGF-1 mirrors GH excesses and deficiencies, but the level in the blood is stable throughout the day, making it a useful indicator of average GH levels.
IGF-1 may be ordered with other pituitary hormone tests, such as prolactin or FSH and LH, to help diagnose pituitary gland dysfunction and decreased pituitary hormones (hypopituitarism).
IGF-1 testing and a GH suppression test can be used to detect and monitor treatment of a GH-producing pituitary tumor. An anterior pituitary tumor is typically confirmed with imaging scans that help identify and locate the tumor. If surgery is necessary, GH and IGF-1 levels are measured after the tumor’s removal to determine whether the entire tumor was successfully removed. Drug and/or radiation therapy may be used in addition to, or sometimes instead of, surgery to try to decrease GH production and return IGF-1 to a normal or near normal concentration. IGF-1 may be ordered to monitor the effectiveness of this therapy at regular intervals for years afterward to monitor GH production and to detect tumor recurrence.
IGF-1 levels and the measurement of GH can also provide information related to GH insensitivity. Prior to performing definitive GH testing, if the IGF-1 level is found to be normal for age and sex, GH deficiency is excluded and definitive testing is not necessary.