Clinical risk indices, prediction of osteoporosis, and prevention of fractures: diagnostic consequences and costs

The primary aim of this study was to validate the Osteoporosis Self-Assessment Tools for Asians (OSTA) instrument in Thai women, and to evaluate its utility in terms of economic costs and fracture prediction. Femoral neck and lumbar spine BMD was measured by dual energy X-ray absorptiometry in 322 Thai women, aged 60 +/- 10 years (mean +/- SD; range: 45-84 years). The women were classified as having osteoporosis if their BMD T -scores were <=-2.5. The OSTA score was calculated for each woman using her age and weight according to the formula: 0.2(weight-age). Women with OSTA scores <=-1 and >-1 were classified as "high risk" and "low risk," respectively. The prevalence of osteoporosis was 33% by femoral neck or lumbar spine BMD. Using the OSTA score, 165 (51.2%) women were classified as high risk. The sensitivity, specificity and positive predictive value of OSTA was 82% 64% and 53%, respectively. If the OSTA score is used to identify women with high risk of fracture, and assuming that the incidence of fracture among osteoporotic and non-osteoporotic women are 2% and 1% per year, respectively, the OSTA score can identify 59% of fracture cases correctly, and 41% are expected to be missed. Furthermore, if the high-risk subjects identified by OSTA are to be treated, and if the treatment reduces fracture incidence by 50%, and assuming that the treatment cost is $1 per day, then the cost to prevent one fracture is estimated to be $48,530. Results of this study suggest that, in the Thai population, the OSTA score had high sensitivity but low specificity and low positive predictive value in the identification of osteoporotic women. Its use in the general population can result in a high false-positive rate and incur significant cost to the community.