Doctors use bone mineral density, or BMD, tests to determine your level of bone mineral density. While BMD can be affected by a variety of factors, the World Health Organization has created a standard score with which to measure bone density with. By standardizing these scores, the WHO has created a universal way for medical professionals to determine normal bone mineral density numbers using the T-score and Z-score.
Normal T-Scores
T-scores reflect how many standard deviations above or below the average peak bone density for a healthy 30 year old adult a patient's BMD tests results are. Normal bone density numbers or T-scores fall between +1 and -1. According to the National Osteoporosis Foundation, "For most BMD tests, 1 standard deviation difference in a T-score equals a 10 to 15 percent decrease in bone density."
Normal Z-Scores
In addition of T-scores, BMD tests results also include a Z-score. The Z-score, as defined by the WHO, is the average bone density for a patient's age and sex group. The average person has a Z-score of zero. Typically, experts only recommend using Z-scores in younger men, pre-menopausal women and children. This is because a low BMD is common in older adults, making Z-scores less accurate than T-scores.
Changes in Bone Density Numbers
Normal bone mineral density numbers do not stay the same through out a lifetime. Bone is its densest by the age of 30. After that, bones will slowly lose density over time. Other factors that can contribute to the rate of bone loss is age, hereditary, sex, diet, exercise, medications and medical maladies.
Maintaining Normal Bone Density Numbers
Keeping a healthy bone mineral density number is important in the prevention of osteoporosis. While it is impossible to completely stop all bone loss, it is possible to slow down bone loss and reduce the risks of osteoporosis. According to the NIH Osteoporosis and Related Bone Diseases National Resource Center, eating foods high in calcium and vitamin D and doing weight-bearing exercise like walking, jogging or dancing can help maintain healthy bone density numbers.
Testing for Normal Bone Density
Testing for BMD is a simple, noninvasive medical test, using X-ray technology to asses your risk of osteoporosis by measuring how many grams of calcium and other bone minerals are in a segment of bone. Bone mineral density scanning, also known as dual-energy x-ray absorptiometry (DXA) or bone densitometry, is typically performed on the lower spine and hips. This simple, painless out-patient procedure determines your bone mineral density.
