In 1994, the World Health Organization (WHO) reviewed the worldwide data on bone density testing and fracture risk. Prior to this publication, many bone density testing centers reported results by comparing a patient to other patients of the same age. The WHO concluded that, based on studies of older women, reporting the relation of the bone mineral density (BMD) to the average peak bone mineral density of a 30-year old would be more appropriate.
The WHO suggested that a BMD result from either the spine or hip that is better than one standard deviation below the average peak BMD of a 30-year old indicates normal bone density. (T-score ≥ -1.0 = normal) A T-score that is worse (or lower) than one standard deviation below the average peak BMD of a 30-year old, but better than 2.5 standard deviations below is considered low bone mass (sometimes referred to as osteopenia). (T-score between –1.0 and -2.5). A value worse than or equal to 2.5 standard deviations below (T-score ≤ -2.5) the average peak BMD of a 30-year old indicates osteoporosis. If the BMD measurement is classified as osteoporosis and the patient has a low trauma fracture, then the patient is said to have established (or severe) osteoporosis.