Your BMD value may also be compared to
other people of your age, sex, and race. This is called your Z-score. It is
given in standard deviations (SD) from the average value for your age
A negative (-) value means that your bones
are thinner (lower bone density) and weaker than most people in your age group.
The more negative the number is, the less bone density you have compared with
others in your age group.
A positive (+) value means that your
bones are thicker and stronger than most people in your age group.
What Affects the Test
Reasons you may not be able to
have the bone mineral density (BMD) test or why the results may not be helpful include:
Inability to be correctly positioned during the
Having a broken bone in the past. This can cause
falsely high BMD results.
Arthritis of your spine. In this case, the changes
caused by arthritis in the spine may not make the spine the best place to
measure for osteoporosis.
Metal implants from hip
replacement surgery or hip fracture.
Having an X-ray test
barium within 10 days of the BMD test.
What To Think About
Experts disagree about which bones are best to
use for BMD measurements. Bones in the
lower spine and
hip are tested most often. These bones generally have
the most bone loss and are more likely to fracture. Sometimes bones in the
wrist are measured. Ultrasound screening is done on the bone in the
A BMD measurement should be done only when the information
provided by the test will affect treatment decisions. BMD does not need to be
measured more often than every 2 years to find out how well treatment is
Using DEXA to measure bone mineral density is replacing
older methods, such as dual photon absorptiometry (DPA).
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.
If your bone
density is lower than normal, you can increase bone density and strength by
taking calcium and
vitamin D supplements, exercising, lifting weights or
using weight machines, and taking some medicines. For more information about
how you can increase your bone strength and density, see the topic
In the United States, legislation (called the
Bone Mass Measurement Coverage Standardization Act) requires Medicare to pay
for bone mineral density testing for people who have Medicare benefits and are
at risk for losing bone mass. This includes:
Women who have gone through menopause and
are at high risk for a bone fracture.
People who have increased
bone loss (osteopenia) or have broken a bone because they have