Bone densitometry guide
http://www.allieddiagnostics.net/patient-guides/bone-densitometry-guide/
The GE DEXA bone densitometer is used to measure a patient’s Bone Mineral Density (BMD). The DEXA scanner is considered the gold standard among health care professionals for measuring bone loss and assessing osteoporosis and risk of future fracture. It is a table scanner that uses two energy levels of low-dose x-ray to quickly measure the bone density of several skeletal sites including the wrist, hips and spine.
How do I prepare for my scan?
There is no need for any special preparation, you may eat normally and you can take the scan fully clothed. However, it is recommended that you do not take calcium supplements 12 hours before your study.
What can I expect during my bone study?
You will be asked to lie still on a padded table, and breathe normally. It is an open scan, so there is no need to worry about closed spaces.
The radiographer may place special pads underneath or alongside your body to ensure proper positioning and comfort. The scan lasts for several minutes whilst the arm of the machine passes over the region of your body being scanned.
Is bone density testing safe?
Yes, the procedure is completely non-invasive and exposure to radiation is small, equaling 1/10th of the amount received from a chest x-ray, or the amount of naturally occurring background radiation encountered in one week. However, because of the risks of radiation exposure to the fetus, pregnant women are advised to avoid this procedure.
How do I know if I have osteoporosis from my bone mineral density score?
Once the examination is completed, a computer will compare your bone strength and risk of fracture to the average value for ‘young normal’ adults and the average for your age-matched peers.
The World Health Organization (WHO) has established the following classifications to categorize patients as normal, osteopenic or osteoporotic based on bone density scores at any skeletal site in white women.
Normal: T-score greater than -1
Osteopenia: T-score between -1 and -2.5
Osteoporosis: T-score below -2.5
Note: The relationship between BMD and fractures in other patient populations such as young women, ethnic minorities, or men has not been established; thus, these WHO classifications are guidelines for all other non-white patients.
What is a T-score?
BMD values obtained from different skeletal sites (e.g. spine and wrist) cannot be directly compared. Instead, these values are discussed in terms of standard deviation (SD). A T-score for BMD is equal to the number of SD above or below the average value for ‘young normal’ adults. For example, if Patient A has a T-score of 1.5, this means she scored 1.5 SD above the average ‘young normal’ adult. If Patient B has a T-score of -2, then she is 2 SD below the average ‘young normal’ adult. For most BMD tests, one SD is equal to 10% to 12% of the average ‘young normal’ adult’s value. In the above examples, Patient A scored 15% to 18% above the average whereas Patient B scored 20% to 24% below the average.
What is a Z-score?
BMD values can also be expressed as Z-scores, which are also discussed in terms of SD. A Z-score is the number of SD above or below the average BMD value for an age-matched peer (i.e. someone the same age as the measured patient). Z-scores are generally not used for discussing a patient’s risk of fracture. Instead, T-scores are preferred because it is when BMD decreases from ‘young normal’ levels that the risk of fracture increases. Abnormalities in BMD are very common in older adults; thus, comparing the patient to persons the same age can be misleading. Z-scores are useful for letting a patient know how s/he compares with someone of the same age.
When will I get the results?
The results of your scan will be sent to your referring physician within 24 hours of your exam. Your report and images will include a summary of the radiologist’s findings and recommendations for further follow-up.
Bone Densitometry Guide [PDF]." class="PDF">Download this guide in PDF format
