IGF-1 is measured to help diagnose the cause of growth abnormalities and to evaluate pituitary function. It is not diagnostic of GH deficiency but may be used along with GH stimulation tests to offer additional information. IGF-1 levels and the measurement of GH can also provide information related to GH insensitivity.
IGF-1 may be used with other pituitary hormone tests, such as adrenocorticotropic hormone (ACTH), to help diagnose hypopituitarism. It may be used to monitor the effectiveness of treatment for growth hormone deficiencies and growth hormone insensitivity.
IGF-1 testing and a GH suppression test can be used to detect a GH-producing pituitary tumour. Presence of a tumour is confirmed with imaging scans that help identify and locate the tumour. If surgery is necessary, GH and IGF-1 levels are measured after removal of the tumour to find out whether or not all of it 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 normal or near normal concentrations. IGF-1 may be used to monitor the effectiveness of this therapy at regular intervals for years afterward to monitor GH production and to detect tumour recurrence.
IGF-1 testing may be used, along with a GH stimulation test, when a child has symptoms of GH deficiency, such as a slowed growth rate and short stature. They also may be requested when adults have symptoms that the doctor suspects may be due to a GH deficiency. An IGF-1 also may be used when a doctor suspects that a person has an underactive pituitary gland and at intervals to monitor patients on GH therapy.
When a GH-producing pituitary tumour is found, GH and IGF-1 are used after the tumour is surgically removed to find out whether all of the tumour has been removed. IGF-1 is also used at regular intervals when a patient is having drug and/or radiation therapy that is frequently used follow tumour surgery.
IGF-1 levels may be requested at regular intervals for many years to monitor a patient’s GH production and to watch for recurrence of a pituitary tumour .
Normal concentrations of IGF-1 must be considered in context. Some patients can have a GH deficiency and still have a normal IGF-1 concentration.
Decreased IGF-1 If IGF-1 concentrations are decreased, then it is likely that there is a deficiency of GH (GH Deficiency; GHD) 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 concentrations may reflect a GH deficiency or insensitivity.
If a decrease in IGF-1 is due to a more general decrease in pituitary function (hypopituitarism), then several of the patient’s pituitary hormones will need to be evaluated and may be supplemented to bring them up to normal levels. Reduced pituitary function may be due to inherited defects or can rise 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 oestrogen.
Increased IGF-1 Elevated levels of IGF-1 usually indicate an increased production of GH. Since GH levels vary throughout the day, IGF-1 concentrations are a reflection of average GH production, not of the actual amount of GH in the blood at the time of sampling. This is accurate up to the point at which the liver’s capacity to produce IGF-1 is reached. With severely increased GH production, IGF-1 levels will stabilise at an elevated maximum concentration.
Increased concentrations of GH and IGF-1 are normal during puberty and pregnancy but otherwise are most frequently due to pituitary tumours (usually benign). If other pituitary hormones are also abnormal, then the patient may have a condition causing general hyperpituitarism.
If IGF-1 is still elevated after the surgical removal of a pituitary tumour, then the surgery may not have been fully effective. Decreasing IGF-1 concentrations during subsequent drug and/or radiation therapies indicate that the treatment is lowering GH production. If levels of IGF-1 return to normal then the patient no longer produces excess amounts of GH. When a patient has long term monitoring, an increase in IGF-1 levels may indicate a recurrence of the pituitary tumour.
If an IGF-1 level is normal and the doctor still strongly suspects GH deficiency, then they may request another test, such as an IGFBP-2 or IGFBP-3 (insulin-like growth factor binding protein 2 or 3), to help confirm the GH deficiency.
This article was last reviewed on 12 July 2016. | This article was last modified on 12 July 2016.
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