DEXA: Dual Energy X-ray Absorptiometry
The most widely test used to screen for osteoporosis is a bone density test (densitometry) that uses an enhanced X-ray technology called dual-energy x-ray absorptiometry (DXA or DEXA). This is NOT the same as a bone scan, which relies on a radioactive injection to help detect areas of increased bone metabolism due to fracture, infection or tumors.
During a bone density test, a low energy source is passed over the body. Information evaluated by a computer allows an estimate of bone mass. This helps the doctor get an idea of bone strength, osteoporosis and risk of fracture.
The results of a DEXA bone density test are interpreted by a radiologist and and report is sent to the doctor who ordered the test. The results will have two scores or numbers.
Understanding the Scores (<--click here)
Your T-score compares you to a young adult of your gender with peak bone mass. Any T-score larger than -1 is considered normal.
The Z-score reflects the amount of bone you have compared to other people your same size, age and gender. This number is related to percentiles. Originally, only Z-scores were calculated, but when bone density machines became commercially available beginning in the 80's, T-scores were devised because different manufacturers could not agree on a standard measurement. You can read about calculating and interpreting both scores here.
Still confused about what DEXA scores mean - in simple terms? Read this from the NIH.
How to read DEXA reports
There are step-by step directions on how to read DEXA reports in this tutorial.
Checking against previous BMD results to assess if the rate of loss has slowed may show the turnaround.. see also..
Problems With DEXA Scores
The reproducibility of DEXA scores is frequently reported at 1-2 percent. That 1-2 percent is the average, but the range of reproducibility can vary as much as 7 percent. Variations come from changes in machine reading (using the same machine), technologists who are doing the test, and slight changes and body positioning, all of which can affect the end results. The most frequent source of error in repeat tests is patient positioning. The technology is limited because BMD is a two-dimensional image of a three-dimensional object.
A few more issues related to DEXA scores are covered in this Wikipedia article which says, inter alia, "It is important for patients to get repeat BMD measurements done on the same machine each time, or at least a machine from the same manufacturer. Error between machines, or trying to convert measurments from one manufacturer's standard to another can introduce errors large enough to wipe out the sensitivity of the measurments."
This Medscape article (registration required, but it is free) reviews the uses and limitations of BMD measurements and the relationship between BMD and bone strength.
Meds to Avoid:
When patients with an elevated level of 1,25-D are given Fosamax (or other biphosphanates), it can cause calcium deposition into the soft tissues, reduced organ function and possible osteonecrosis of the jaw (ONJ). All these meds have some effect on the immune or endocrine system and are, therefore, to be avoided.
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* We can help you understand chronic disease, but only your physician is licensed to give you medical care * Always consult your physician before commencing or changing any treatment he/she has prescribed for you
