September 3, 2015
Osteoporosis, the most common of all metabolic bone disorders, is defined by the World Health Organization (WHO) as “a skeletal disease, characterized by low bone mass and micro- architectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture” [1-3]. WHO created an operational definition of postmenopausal osteoporosis based on T and Z score measurements of Bone Mineral Density (BMD) with dual energy X-ray absorptiometry (DXA). According to the ranking system of WHO postmenopausal women are categorized as: 1) normal: if BMD value is of not less than one Standard Deviation (SD) than the average young adult’s (T-score>-1), 2) osteopenic: if BMD value is between one and 2.5 SD below
the average for young adults (-1<T-score<-2.5), 3) osteoporotic: if BMD value is 2.5 SD or more below the average for young adults (T-score>-2.5) and 4) women with severe or established osteoporosis: if BMD value is 2.5 SD or more below the average for young adults and one or more fractures are present [3,4]. A similar categorization exists for Z-scores. The Z-score is the number of standard deviations above or below what is normally expected for someone of similar age, sex, weight and race in question. In clinical practice, it is useful
because a Z-score of below -1.5 SD probably indicates secondary causes of osteoporosis .