Less commonly, IGF-1 tests may be used to detect excess growth hormone and to help diagnose and monitor treatment of two rare conditions, acromegaly and gigantism.
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.
A child has symptoms of GH deficiency, such as a slowed growth rate and short stature
Adults have symptoms that a health practitioner suspects may be due to a GH deficiency, such as decreased bone density, fatigue, adverse changes to lipid levels, and reduced exercise tolerance. However, testing for IGF-1 deficiency is not routine in adults who have these symptoms; GH and IGF-1 deficiency are only very rare causes of these disorders.
An IGF-1 also may be ordered when a health practitioner suspects that someone has an underactive pituitary gland and at intervals to monitor those on GH therapy.
When a GH-producing pituitary tumor is found, GH and IGF-1 are ordered after the tumor is surgically removed to determine whether all of the tumor has been extracted. IGF-1 also is ordered at regular intervals when someone is undergoing the drug and/or radiation therapy that frequently follow tumor surgery.
IGF-1 levels may be ordered at regular intervals for many years to monitor a person's GH production and to watch for pituitary tumor recurrence.
A normal level of IGF-1 must be considered in context. Some people can have a GH deficiency and still have a normal IGF-1 level.
Decreased IGF-1 If the IGF-1 level is decreased, then it is likely that there is a GH deficiency or an insensitivity to GH. If this is in a child, the GH deficiency may have already caused short stature and delayed development and may be treated with GH supplementation. Adults will have an age-related decrease in production, but lower than expected levels may reflect a GH deficiency or insensitivity.
If a decrease in IGF-1 is suspected to be due to a more general decrease in pituitary function (hypopituitarism), then several other endocrine glands and their pituitary regulating hormones will need to be evaluated to decide on appropriate treatment. Reduced pituitary function may be due to inherited defects or can develop as a result of pituitary damage following conditions such as trauma, infections, and inflammation.
Decreased levels of IGF-1 also may be seen with nutritional deficiencies (including anorexia nervosa), chronic kidney or liver disease, inactive/ineffective forms of GH, and with high doses of estrogen.
Increased IGF-1 Elevated levels of IGF-1 usually indicate an increased production of GH. Since GH levels vary throughout the day, IGF-1 levels are a reflection of average GH production, not of the actual amount of GH in the blood at the time that the sample for the IGF-1 measurement was taken. This is accurate up to the point at which the liver's capacity to produce IGF-1 is reached. With severely increased GH production, the IGF-1 level will stabilize at an elevated maximum level.
Increased levels of GH and IGF-1 are normal during puberty and pregnancy but otherwise are most frequently due to pituitary tumors (usually benign).
If IGF-1 is still elevated after the surgical removal of a pituitary tumor, then the surgery may not have been fully effective. Decreasing IGF-1 levels during subsequent drug and/or radiation therapies indicate that the treatment is lowering GH production. If levels of IGF-1 become "normalized," then the person is no longer producing excess amounts of GH. When someone is undergoing long-term monitoring, an increase in IGF-1 levels may indicate a recurrence of the pituitary tumor.
If an IGF-1 level is normal and a health practitioner still strongly suspects a GH deficiency, then the healthcare provider may order another test, an IGFBP-3 (insulin-like growth factor binding protein 3), to help confirm the GH deficiency. Almost all IGF-1 in the blood is bound to binding proteins, with IGFBP-3 being the most prevalent form, and IGFBP-3 production is also stimulated by GH.
This article was last reviewed on March 23, 2015. | This article was last modified on March 23, 2015.
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