How to Read Your Bone Density Test

According to the Mayo Clinic, bone fracture, particularly of the hip, is one of the most prevalent causes of illness among the elderly and frequently results from a loss of bone density---osteoporosis. A bone density test, also called a bone mineral density (BMD) test can predict the risk of bone fracture in post-menopausal women. According to a 2005 study in the "Journal of Endocrinological Investigation" there is still some uncertainty whether the scoring can predict fracture in men as well as it does in women.

Difficulty: Moderately Easy

Instructions

1. Request a copy of the actual laboratory results from the dual-energy x-ray absorptiometry bone density test, commonly called a DEXA test. It should contain two scores, a T-score and a Z-score.

2. Refer to the T-Score, which represents a statistical calculation of the number of standard deviation units above or below the average bone density of a normally healthy young woman.

3. Consider your bone density normal if it is above minus-1. Interpret the score as indicating osteopenia, that is, lowered bone density if it is a number smaller than minus-1 (for example minus-1.5) but greater than minus-2.5.

4. Read a T-Score that is smaller than minus-2.5 (for example, minus-3) as an indication of osteoporosis.

5. Note the second score, the Z-score. This compares your bone density to the average reading for other individuals sharing your age range and gender. If your Z-score equals zero, then it matches the average, placing you in the 50 percentile. That is, 50 percent of your Z group have better bone density and 50 percent have less.

6. Use the percentile table provided by the University of Washington in their Web explanatory reference "Osteoporosis and Bone Physiology" to translate your Z-score to a percentile ranking. As an example, a Z-score of minus-0.68 places an individual in the 25th percentile, which means 75 percent of the comparable group has a higher bone density. A Z-score of plus-0.68 puts a person in the 75th percentile, which indicates an individual probably at less bone fracture risk than 75 percent of the age/sex group.

Tips & Warnings

• In general, a Z-score at the hip indicates a relative risk of fracture of about two-and-one-half times for each deviation from the average score.
• Different bone density measuring machines use slightly different ways of measuring. Reference ranges for Z-scores differ from one site to another as well. Some may include an average group based on more than age and sex, for example race, or even weight. Therefore, no one can compare their own T and Z-scores to someone else without knowing which type of equipment was used and how the scores are calculated.

References

• Bone Density Test
• "Journal of Endocrinological Investigation"
• T and Z Scores

Resources

• National Osteoporosis Foundation

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