A bone density chart shows normal bone mass levels versus levels associated with osteoporosis, says the National Institutes of Health. A bone density chart categorizes the numbers from a bone marrow density test, or BMD, using the ideal bone density of a healthy 30-year-old as the standard.
Bone marrow density test results are expressed as a number called a T-score, explains the National Institutes of Health. A BMD score of zero or -1/+1 means bone density is equal to that of a healthy young adult, while a score of -1 to -2.5 means bone mass is low. A score of -2.5 or lower indicates osteoporosis, which increases the risk of a bone fracture. When BMD results fall into the low bone mass category on a density chart, it's called osteopenia, and although this condition doesn't necessarily develop into osteoporosis, it's an indicator of greater risk. Underdeveloped peak bone mass during youth, heredity, medical conditions that affect bone density and accelerated deterioration are factors that influence bone loss.
A BMD usually evaluates bones most at risk of fracturing due to osteoporosis, notes Mayo Clinic. These include the forearm, thigh bone and lower spinal vertebrae. Devices that test bone density in the hands and feet are available in pharmacies, but the medical community does not consider the results to be accurate indications of osteoporosis.