How do doctors interpret a Bone Mineral Density (BMD) Report?
A. DXA (dual energy x-ray absorptiometry) measures bone mass at two sites – the lumbar or lower spine and the hip. The vertebrae or bones of the spine all have numbers. The test looks at the bones L1 to L4. DXA looks at several areas of the hip most notably the femoral neck. To diagnose osteoporosis, doctors traditionally focus on the measurements at L1 to L4 and the femoral neck. They compare the bone mass with two different standards. The first comparison is with young adults of the same sex. This provides a measure of peak bone mass called the T-score. The second comparison is to age, weight, sex and race-matched controls. This is known as the Z- score. For a given BMD, the T-score is the number of standard deviations (SD) below the mean of young adult controls. (A standard deviation is a consistent unit of measure above or below a zero point that is considered normal). The Z-score gives the SD below the mean of age-matched controls. A committee of the World Health Organization has
