A bone density scan is a way to measure the strength of your bones. The test, also called a DEXA scan, uses X-rays to measure how many grams of calcium and other bone minerals are packed into a segment of bone. 

The bones that are commonly tested are the spine, hip and sometimes the forearm. The test calculates your bone mineral density and translates this value into a number. This number can be compared to your subsequent scans to determine the effects of osteoporosis on your body. Your bone mineral density (BMD) is also compared to reference standards to determine if you are at risk for fractures. 

Low bone density is usually caused by osteoporosis resulting in reduced bone strength or “brittle bones”. The bone density test is painless and uses a very low dose of radiation.