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and to evaluate pituitary function. It is not diagnostic of GH
deficiency but may be ordered 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 ordered 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 tumor. Its presence is then 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 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 tumor recurrence.
When is it ordered?
IGF-1 testing may be ordered, 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 ordered when adults have symptoms that
the doctor suspects may be due to a GH deficiency. An IGF-1 also may be
ordered when a doctor suspects that a person has an underactive
pituitary gland and at intervals to monitor patients on GH therapy.
IGF-1 testing may be ordered, along with a GH suppression test, when a
child has symptoms of gigantism, an adult shows signs of acromegaly,
and/or when a doctor suspects that a patient has hyperpituitarism.
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 a patient 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 patient's GH production and to watch for pituitary tumor
recurrence.
What does the test result mean?
NOTE: This test has no single number that identifies an abnormal
result. Your lab report (see a sample report) should include a range of
numbers (reference range) that identifies what is expected for you
based on your age, sex, and the method used in that laboratory. You can
find more information about expected results at Reference Ranges and
What They Mean. Lab Tests Online strongly recommends that you discuss
the meaning of your test results with your doctor.
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
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 concentrations are a
reflection of average GH production, not of the actual amount of GH in
the blood. 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 stabilize 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 tumors
(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
tumor, 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 become ?normalized,? then the patient is no longer producing
excess amounts of GH. When a patient is undergoing long term
monitoring, an increase in IGF-1 levels may indicate a recurrence of
the pituitary tumor.
Is there anything else I should know?
If an IGF-1 level is normal and the doctor still strongly suspects a GH
deficiency, then he may order another test, an IGF BP 2 or IGF BP 3
(insulin-like growth factor binding protein 2 or 3), to help confirm
the GH deficiency.
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