Bone Mineral Density

A bone mineral density (BMD) test measures the mineral density such as calcium in your bones using a special  X-ray scan.  From this information, an estimate of the strength of your bones can be made.

Calcium is constantly being added to and taken away from bone. When calcium is taken away faster than it is added, the bones become lighter, less dense, and more porous.  This makes the bones weaker and increases their risk of fracture.

Loss of bone mass occurs as part of the natural process of aging. Bones naturally become thinner as you grow older, because existing bone is broken down faster than new bone is made.  This process is called osteopenia.  As this occurs, the bones lose minerals, heaviness, and structure, making them weaker.  With further bone loss, osteopenia develops into osteoporosis.  The thicker your bones are, the longer it takes to develop osteoporosis.  Although osteoporosis can occur in men, it is most common in women older than age 65.

Regular X-rays cannot detect mild bone loss.  A bone must lose at least a quarter of its weight before a regular X-ray can detect the problem.

Controversy exists over which bones are best to use for BMD measurements. The bones most commonly used are those in the lower spine and hip.  These bones generally have the greatest amount of bone loss and are at the highest risk of fracture.  In special cases, bones in the wrist may be used.

Here at Texas Cancer Clinic we use Dual-energy X-ray absorptiometry (DEXA) to determine Bone Mineral Density.  DEXA uses two different X-ray beams to estimate bone density in your spine and hip. The amounts of each X-ray beam that are blocked by bone and soft tissue are compared to each other. Bones with higher mineral density allow less of the X-ray beam to pass through them. DEXA is the most accurate method for measuring BMD.  DEXA can measure as little as 2% of bone loss per year.  It is fast and uses very low doses of radiation.