Bone mineral density is a measure of the amount of minerals contained in a certain volume of bone. Calcium gives bones their strength and helps prevent fractures. A bone mineral density test, also called a bone mass measurement, is used to measure bone density and determine fracture risk for osteoporosis. It may also be used to determine how effective an osteoporosis treatment is. The National Osteoporosis Foundation recommends BMD testing...
Useful...? Yes as a diagnostic tool.
A density test is usually performed as a simple X-ray of the wrist. It measures the "hardness" of the bone. For ankylosing spondylitis...