Osteoporosis Testing: Bone Density Tests
Information on Osteoporosis Screening: DEXA Scans & T Score Results
Nov 8, 2009
Bone density screening tests are officially known as Dual Energy X-Ray Absorptiometry, DEXA or DXA for short. DEXA scanning is a fast, accurate and easy way of testing for osteoporosis and is covered by most insurance.
Bone Density Screening: DEXA Scans
Osteoporosis bone density tests like DEXA scans measure bone density in two locations, normally the hip and lower spine, although the wrist can be used if good measurements can’t be obtained at the other sites. Results of bone density screening are given as a T or Z score. T scores compare a person’s bone density to the bone density of an average young adult age 25-35, and Z scores compare bone density to other people of the same age, sex, height and weight.
What Happens During a DEXA Scan
Having a DEXA test is simple. There’s no advance prep except to refrain from taking calcium supplements, including antacids, the day before and the day of the DEXA scan. This is because calcium supplements may give an artificially high bone density reading.
A DEXA scan takes about 15 minutes of lying on a table fully dressed. People having DEXA scans should avoid wearing clothes with metal zipper or decoration, and should remove jewelry, since metal can give a higher than normal reading.The radiation used for a DEXA can is quite minimal, about 1/30th of what would be used for a chest X-ray.
Interpreting T Score Results After Bone Density Screening
T score results are obtained by this formula:
Person’s bone mineral density minus a young normal mean (average) divided by standard deviation of young normal mean.
That may sound clear as mud; it means simply that the difference between an average young person’s bone density and the patient’s bone density is the standard deviation (SD), which is called a T score. For scoring purposes:
A score of 0 (zero) means a person’s bone density is equal to that of an average young person of the same sex and ethnicity.
A score of -1 means a lower bone density score compared to an average young person. The lower the T score, the more severe osteoporosis. The formula is:
- normal T score= 1 SD or less below the average young person, or up to -1
- osteopenia, or low bone mass= 1-2.5 SDs below the average, or -1 to -2.5
- osteoporosis= 2.5 or greater SD below average, or -2.5 or lower
- severe osteoporosis= -2.5 or less on T score and the presence of one or more bone fractures
Doctors look at the lowest score obtained, so if the hip reading is lower than the spine reading, that’s the one they’ll use to determine treatment for osteoporosis. Z scores are read the same way as T scores, except that a lower Z score is more serious, because it compares the patient to another person of the same age rather than to someone younger.
Benefits of Having Regular Bone Mineral Density Testing (DEXA Scans)
Having a bone density test done every two years, or more often if necessary, helps ensure that any change in bone density is promptly addressed and treated. Understanding T scores is beneficial for compliance in treating osteoporosis.
Source:
Bone Densitometry for Technologists, Sydney Lou Bonnick, Lori Ann Lewis; Humana Press 2006
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