DXA – The Old Standard
DXA has been the standard screening test for Osteoporosis in the USA for two decades. DXA is easy to obtain and the computer print-out makes it look very simple to read. Too simple if all you do is look at the computer print-out. DXA is not the whole story. And that is not the only difficulty.
DXA measures Bone Mineral Density (BMD). Calcium is the usual mineral in bone, and the one we intend to measure. The computer reads out calcium g/cm2 (a bit hard to understand) and also gives a “t-score” comparing the test result to a healthy 30 year old woman. That makes it simple – “normal”, “osteopenia”, or “osteoporosis”. Again, much too simple if what you really want to know is Fracture Risk.
FRAX (Fracture Risk Assessment Tool) is much more accurate than DXA alone because it takes into account other fracture risk factors, such as age. When DXA is used it counts for 30% of the calculation. That is because calcium content of bone is not the whole story in assessing for “Clinical Osteoporosis” or high fracture risk. And there is another problem with DXA and BMD – accuracy.
Arthritis and vertebral deformity of the spine, or improper positioning of the hips, due to arthritis or other issues, can make the BMD look much better than it is. No DXA computer programs have been updated to take these details into account. You need a human to over-read the computer. That is where the International Society for Clinical Densitometry (ISCD) comes in. ISCD has developed protocols that make DXA more accurate. Ask for an ISCD Certified Clinical Densitometrist reading for your DXA.
And then there is VFA…….
Jay Ginther, MD