Hormones
IGF-BP3
The protein that binds the growth factor IGF-1 in the blood; follows the activity of growth hormone, but less sharply than IGF-1 itself.
Everything about this testWhat it measures
IGF-BP3 (insulin-like growth factor-binding protein 3) is the main protein to which IGF-1 is bound in the blood; by far most IGF-1 circulates in a complex with IGF-BP3. The liver makes IGF-BP3, just like IGF-1, under the influence of growth hormone from the pituitary gland. As a result, the value follows the average activity of growth hormone and is stable over the day. The value depends strongly on age: high during puberty and then gradually lower.
- Too much growth hormone (acromegaly), as an addition to IGF-1
- A shortage of growth hormone, especially in children with delayed growth, together with IGF-1
- Monitoring of treatment with growth hormone
- Use of growth hormone or of substances that stimulate its release
High
A high value is normal during puberty. In adults, a raised value is often due to the use of growth hormone or substances that stimulate its release. The value can also be higher with reduced kidney function. A value that is clearly too high for your age, together with a raised IGF-1, may fit acromegaly: too much growth hormone due to a usually benign tumor of the pituitary gland, with slowly enlarging hands and feet, coarsening facial features and heavy sweating.
Low
IGF-BP3 gradually falls with age; a lower value in older people is usually normal. Malnutrition, rapid weight loss, liver disease, poorly controlled diabetes, an untreated underactive thyroid and estrogens taken by mouth can lower the value. A low value may fit a shortage of growth hormone, for example due to a damaged pituitary gland, but does not prove it; that requires a stimulation test.
If your result is abnormal
With an abnormal value, the GP usually has IGF-1 measured and looks at age, diet, illnesses and medicines. With an IGF-1 that is too high for your age and matching symptoms, you are referred to an internist-endocrinologist; a child with delayed growth is referred to a pediatrician. A slightly abnormal value without symptoms usually does not lead to further testing.
Reliability
IGF-BP3 follows the activity of growth hormone less sharply than IGF-1 and overlaps more between people with and without a disorder. In adults, IGF-1 says more when something is abnormal, both when acromegaly is suspected and when monitoring treatment. In children with delayed growth, IGF-BP3 can help together with IGF-1, because IGF-1 is naturally low in young children. A shortage or excess of growth hormone is only confirmed with a stimulation test or glucose drink test. As a measure of fitness or aging, IGF-BP3 is not supported by evidence.
Limitations
- Age: the reference values differ strongly by age group; a result can only be interpreted against the limits for that age.
- Measuring methods give different results from each other; preferably compare results from the same laboratory.
- Nutritional status, liver and kidney function, thyroid function and diabetes affect the value.
- Growth hormone and substances that stimulate its release raise the value; estrogens taken by mouth lower it.
How common is this
Acromegaly is rare: in the Netherlands, it is diagnosed in about 50 to 100 people per year. A shortage of growth hormone in adults mainly occurs in people with a known pituitary condition or after pituitary surgery or radiotherapy.
Who is this useful for
The result says the most together with IGF-1, in children with delayed growth, with symptoms that fit acromegaly or with a known pituitary condition. Not suitable as a measure of aging, fitness or muscle building in healthy people. In people without symptoms, a single value says little.
Downsides and risks
- A slightly abnormal value without symptoms can lead to unnecessary worry about the pituitary gland and to unnecessary tests such as an MRI.
- A low value is sometimes taken as a reason to use growth hormone; use without a proven shortage has no medical basis and is on the doping list.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results