How does bone density measurement work?
Bone density measurement can be used to determine whether there is a risk of osteoporosis. Osteodensitometry – for those who speak foreign languages, it quickly becomes clear that this means the measurement (“metry”) of the density (“densus”) of the bone (“osteo”). Bone density is a measure of how strong the bone is. It is measured based on the calcium salt content, i.e. the minerals that give the bone its strength. These are primarily calcium phosphate and calcium carbonate. If these are reduced, for example after the menopause , bone loss (osteoporosis) occurs, i.e. a reduction in the mass and stability of the bone.
If osteoporosis is detected in good time, it can be prevented or treated accordingly, thereby reducing the increased risk of fractures  .
Various methods and devices are available for the examination. Dual Energy X-ray Absorptiometry (DXA) is now the standard procedure for measuring bone density and thus determining bone fragility.
Common to all methods is the principle that rays penetrate the bone and are weakened to varying degrees depending on the density, i.e. mineral salt content. This applies both to X-rays (e.g. in computed tomography ) and to ultrasonic waves. In the case of the latter, in addition to the attenuation of the rays, the speed of the sound waves on their way through the bone tissue is also measured.
They have the advantage that they do not expose the patient to radiation; however, their significance has been the subject of controversy for years. Since it is known for each procedure how strong the weakening of the rays is in healthy people, newly measured values ​​can be compared with this standard value.
How does the bone density measurement work?
No patient preparation is required. Depending on the procedure, the person being examined lies down in or under the corresponding device. Bone density is measured in areas that are not covered by other bone sections, especially in the femoral neck and lumbar spine. In the meantime, however, bone density is also sometimes measured on the entire body (full body DXA scanner). Fabric does not interfere, so the bone density measurement takes place with clothing.
However, metal parts in the examined region, such as coins in your trouser pocket, can falsify the measurement result and must therefore be discarded. If an artificial hip joint or other metal parts are present in the body, the examiner must be informed. The entire examination takes between 10 minutes and half an hour. Sometimes the activity of the bone metabolism is also determined using certain substances in the urine. In the case of special questions, a blood sample may also be  necessary.
How is the result evaluated and what bone density is normal?
The personal measured values ​​are compared with normal values ​​of healthy people of the same age (Z value) of the same sex as well as healthy test persons around 30 years of age (T value). The T value thus corresponds to the maximum bone density. Depending on the deviation of the T value, a distinction is made between a normal result, poor bone quality (osteopenia) and bone loss (osteoporosis).
The following T-values ​​apply as a guideline for a bone density measurement:
- Standard deviation ≥ -1: normal finding
- Standard deviation -1 to -2.5: osteopenia (precursor to osteoporosis)
- Standard deviation ≤ -2.5: osteoporosis
If the bone loss is accompanied by typical bone fractures, it is referred to as severe osteoporosis. The T value is therefore used for diagnosis. The Z value, on the other hand, helps in deciding on a suitable therapy: It gives an indication of whether drug therapy may be indicated. However, this decision does not depend solely on the measured value, but is primarily made on the basis of the other medical findings.
Who bears the cost of a bone density measurement?
Unfortunately, an initial bone density measurement is often not covered by health insurance. It is currently only reimbursed by the statutory health insurance companies if the doctor has a reasonable suspicion of this disease and there is at least one broken bone, or if there is a proven increased risk of osteoporosis, for example in the case of chronic kidney failure .
As part of early detection, i.e. without signs of illness, a bone density measurement currently has to be paid for by those affected themselves. The costs for a bone density measurement are billed by the treating doctor on the basis of the fee schedule for doctors (GOÄ). The basic costs are between 18 and 32 euros. There may also be additional costs for consultations.
If the osteoporosis has been diagnosed by a doctor, new bone density measurements will be covered by the health insurance company.
Which doctor performs a bone density measurement?
A bone density measurement is usually carried out by an orthopedist or radiologist. The best thing to do is to ask your general practitioner which practice he can recommend for the measurement.
When and how often will the examination be repeated?
If osteoporosis has been diagnosed and appropriate therapy initiated, its success should be checked. Since bone reconstruction takes a certain amount of time and unnecessary exposure to radiation should be avoided, another bone density measurement using X-rays is recommended after two years at the earliest.
For certain people at very high risk, such as patients on permanent cortisone therapy or after organ transplants, osteodensitometry must be carried out regularly at shorter intervals (semi-annually or annually). In order to be able to compare the examination results with each other, it is advisable to take control measurements on the same device, ideally with the same examiner.
When is a bone density measurement useful?
Basically, a bone density measurement makes sense if symptoms such as long and persistent back pain , loss of height or frequent fractures occur. Different risk factors can also promote the occurrence of osteoporosis. Examples of risk factors are a hormone deficiency during menopause, malnutrition or a family history. Find out in our test  whether you have an increased risk of osteoporosis.
Bone densitometry can also be used to detect – less common – softening of the bones (osteomalacia) as a result of disrupted incorporation of minerals in the bones.
