Bone Density Measurement
Peripheral quantitative computed tomography is a way of measuring bone mineral density in a peripheral part of the body. It is the basis of all osteoporosis diagnoses and can be done with a number of different examination techniques.
The most important procedure is:
DEXA (Dual-energy X-ray absorptiometry)
This method of examination is used particularly on the lumbar vertebrae and femur. It is characterised by a high degree of accuracy, requires relatively low doses of ionising radiation and is regarded as being the ‘gold standard’. It enables bone mineral content to be measured in the area examined.
T-value
The result of the bone density measurement is given with a T-value. The T-value gives the difference in standard deviation between the patient’s measurement and the median value of healthy young adults.
The T-value is normal if it is below the standard deviation for young adults. There is bone mineral content reduction (osteopenia) if the T-value is within a range –1 to –2.5 standard deviation. Patients with less than –2.5 standard deviation have osteoporosis.
Special care is required with the results of the DEXA examination particularly where elderly patients have pronounced deterioration (spondylosis) of the lumbar spine and/or calcification of the aorta, as the high value of the bone mineral content measurement is often misleading.
Classification of osteoporosis according to the results of the DEXA examination, using the T-value
| Prevention areas: | T-values > -1 | Normal findings |
| T-value from -1 to -2.5 | Osteopenia | |
| Therapy area: | T-values < -2.5 | Osteoporosis |
For which groups of people should bone density measurement be carried out?
Carrying out a bone density measurement is generally recommended:
- with clinical evidence of suspected osteoporosis with the presence of at least one or more risk factors
- for women following the onset of the menopause
- for people over 65
Apart from this, those belonging to high-risk groups such as patients on cortisone therapy or after an organ transplant should be examined with DEXA on a yearly basis.