Hormones
Groeihormoon
A pituitary hormone for growth and metabolism; a single measurement says little because it is released in peaks.
Everything about this testWhat it measures
Growth hormone (GH, also called somatotropin) is made in the pituitary gland, a hormone gland below the brain. In children it drives growth in height; in adults it plays a role in muscle mass, bone density and fat metabolism. Much of its effect runs through IGF-1, which the liver makes under the influence of growth hormone. Growth hormone is released in peaks, including during sleep and after exercise, and in between is often barely measurable.
- Acromegaly (too much growth hormone), but only through a suppression test with sugar water in which growth hormone does not fall enough
- A shortage of growth hormone, but only through a stimulation test in the hospital
- Use of growth hormone or of substances that stimulate its release, although a single measurement is unreliable for this
High
A raised single value is usually harmless: it can be a normal peak, for example due to sleep, exercise, stress or fasting shortly before the blood draw. Use of growth hormone or of substances that stimulate its release also gives a higher value. Only if growth hormone does not fall enough after drinking sugar water and IGF-1 is too high for age does it fit acromegaly: too much growth hormone due to a usually benign tumor of the pituitary gland. The symptoms that go with it develop slowly: larger hands and feet, coarsening facial features, heavy sweating, joint complaints and headache.
Low
A low or unmeasurable value is very common in a single measurement, because the value is low between the peaks. Overweight also reduces the release. A low single value therefore does not prove a shortage. A true shortage, for example due to damage to the pituitary gland after surgery, radiotherapy or from a tumor, is established with a stimulation test together with IGF-1, and causes symptoms such as less energy, less muscle strength, a changed body composition and bone loss.
Preparation
- Do not eat anything for 12 hours before the sample is taken and drink only water.
- Have your blood taken in the morning around 8.00, after a good night's sleep.
- Do not exercise and avoid stress shortly before the sample is taken, because that temporarily raises growth hormone.
If your result is abnormal
With an abnormal single value, the GP usually first has IGF-1 measured. With too high an IGF-1 and matching symptoms, a referral to an internist-endocrinologist follows for a sugar water test and, if needed, an MRI of the pituitary gland; if a shortage is suspected, a stimulation test follows. With a normal IGF-1 without symptoms, no follow-up testing is needed.
Reliability
According to the Dutch Society for Clinical Chemistry (NVKC), the peaks and troughs make it impossible to establish with one measurement whether too much or too little growth hormone is being made. That requires a suppression test with sugar water or a stimulation test with arginine or clonidine, which are done in the hospital. IGF-1 is the usual first blood test, because that value is stable over the day. A single growth hormone measurement therefore says little, especially in people without symptoms.
Limitations
- Timing and circumstances: sleep, exercise, stress and fasting temporarily raise the value, making a single value hardly interpretable.
- There are no general cutoff values for a single measurement; thresholds only apply within a suppression or stimulation test and differ per laboratory and test.
- Use of growth hormone or of substances that stimulate its release raises the value; overweight lowers it.
- Measurement methods differ per laboratory, so results are not easily comparable with each other.
How common is this
Acromegaly is rare: in the Netherlands the diagnosis is made 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. In children, lagging growth is usually not caused by growth hormone, but for example by the height of the parents or another illness.
Who is this useful for
A single growth hormone measurement is rarely useful. With symptoms that fit acromegaly or with a known pituitary condition, IGF-1 is the first step; growth hormone is then measured in the hospital during a suppression or stimulation test. Not useful as a measure of aging, fitness, muscle building or recovery, and not for deciding on the use of growth hormone.
Downsides and risks
- A chance peak or, conversely, a trough can wrongly be interpreted as disease and lead to unnecessary worry and follow-up testing.
- A low value is sometimes seen 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