Muscles and bones
Osteocalcine
Osteocalcin is a measure of the rate of bone formation; it is not a test for osteoporosis.
Everything about this testWhat it measures
Osteocalcin is a protein that bone-forming cells (osteoblasts) make and build into bone. A small part ends up in the blood. The more active bone formation is, the higher the value. Bone tissue is broken down and rebuilt throughout life; osteocalcin says something about the rate of formation at that moment, not about how much bone there is. The kidneys clear osteocalcin.
- A raised or lowered rate of bone formation at the time of measurement
- A change in that rate during treatment for osteoporosis
High
A high value fits a high rate of bone formation. This is normal in children and young people who are still growing and in the months after a broken bone. A high value is also seen in the years around and after menopause, with an overactive parathyroid or thyroid gland, with a vitamin D deficiency that softens the bone (osteomalacia) and with Paget's disease. With reduced kidney function the value is higher, because osteocalcin is cleared less well. A high value does not mean that you have osteoporosis.
Low
A low value fits a low rate of bone formation. This is seen with long-term use of prednisone or other corticosteroids and during treatment that slows bone breakdown. A low value does not mean that your bones are strong or weak: the amount of bone is measured with a bone density scan (DXA), not with this marker.
Preparation
- Have your blood taken in the morning between 8:00 and 9:00, because osteocalcin follows a daily rhythm. Have a repeat test done at the same time of day.
- Do you take biotin (vitamin B8, often in hair and nail supplements)? Stop at least 2 days before the sample is taken, or 4 days for a high dose.
If your result is abnormal
With a question about osteoporosis, the GP first estimates the risk of a broken bone and, if needed, requests a bone density scan, with blood tests for underlying causes such as calcium, vitamin D and the thyroid. An abnormal osteocalcin value on its own does not lead to fixed further tests.
Reliability
In an individual, a single value says little about the amount of bone or the risk of a broken bone. Osteoporosis is diagnosed with a bone density scan; the laboratory tests that the guideline on osteoporosis and fracture prevention lists for this look for an underlying cause and do not include bone markers. According to the Dutch Society for Clinical Chemistry (NVKC), reference values for bone markers are hard to give because laboratories differ. The result is most meaningful when repeated in the same person, in the same laboratory and at the same time of day.
Limitations
- Osteocalcin is not stable in blood: the blood must be spun down and frozen quickly, otherwise the result will be too low.
- The value follows a daily rhythm; that is why blood is drawn in the morning at a fixed time.
- Reduced kidney function, a recent broken bone and growth in children and young people raise the value.
- Corticosteroids lower the value; high-dose biotin (vitamin B8) can interfere with the result in some test methods.
How common is this
Osteoporosis is common, especially in women after menopause and in older people. Osteoporosis is diagnosed with a bone density scan, not with bone markers in blood.
Who is this useful for
The result is mainly meaningful with unexplained bone abnormalities or when following treatment for osteoporosis, and then in combination with other tests. It is not a test for osteoporosis: in people without symptoms the result adds nothing to estimating the risk of a broken bone. If you want to know about that, you need a risk assessment and, if needed, a bone density scan.
Downsides and risks
- A high value can wrongly be read as osteoporosis, leading to worry and unnecessary further tests.
- A normal value can be falsely reassuring, while it does not measure the risk of a broken bone.
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