osteoporosis is a systemic skeletal disorder characterized by low bone strength ( arising from both low bone mass and microarchitectural deterioration ) , which increases the risk of fractures .
osteoporosis is a major public health problem and an important contributor to the global burden of noncommunicable disease .
currently the recommended method for the diagnosis of osteoporosis is bone mineral density ( bmd ) measurement by dual - energy x - ray absorptiometry ( dxa ) . according to the world health organization criteria
, osteoporosis is operationally defined  as a bmd that lies 2.5 standard deviations or more below the average value for young healthy women .  .   since
, due to cost and availability , dxa scans are not recommended for screening purposes , several tools based on known clinical risk factors have been developed to identify those patients with high risk of osteoporosis , in whom actual bmd testing would be most useful in terms of diagnosis , treatment , and followup [ 3 , 4 ] . some of these clinical tools , or aids in decision making , include many factors , making calculation of risk cumbersome [ 5 , 6 ] . arguably the simplest decision rule is the osteoporosis self - assessment tool ( ost ) which only takes into account body weight and age , which in adult populations are , respectively , related inversely and directly to the risk of osteoporosis .  
the ost was developed for predicting risk of femoral neck t - score at or below 2.5 in asian postmenopausal women   and later validated for caucasian european and us postmenopausal women . in these populations , the performance of the ost was similar to those of more complex clinical risk assessment tools [ 3 , 1012 ] although a related tool , called osteorisk , has been validated for latin american postmenopausal women , no direct assessment of the ost has been yet performed in this region .
the current prevalence of osteoporosis and the incidence of osteoporotic fractures in latin america are similar to those of southern europe [ 1416 ] , but lower than those of northern europe and the united states [ 1 , 2 ] . however , a significant increase in the incidence of osteoporotic fractures is expected to occur in latin america in the next few years , according to a world health organization report .
this highlights the need for improving clinical assessment and selection of women for bmd testing .   in this report
, the performance of the ost in a sample of postmenopausal women from western argentina was assessed .
the province of mendoza in western argentina has a population of 1,742,000 inhabitants according to the 2010 census . about 62% of the population lives in greater mendoza , the fourth largest metropolitan area of the country , which includes about 133,000 women aged 50 years or older .
the current sample included 4343 women referred to the bone densitometry unit of the nuclear medicine school for a first ( diagnostic ) dxa scan of lumbar spine and hip . women with paget 's disease , primary hyperparathyroidism , or severe hip osteoarthritis
the research protocol was reviewed and approved by the committee of teaching and research of the nuclear medicine school .
the study was planned and conducted in full accordance with the current version ( 2008 ) of the declaration of helsinki .
the height and weight of each patient were measured while she stood without shoes , wearing light clothing . the body mass index ( bmi )
was calculated as her weight in kg divided by her height in m squared ( kg / m ) .  
patients were asked about previous fragility fractures , glucocorticoid , estrogen or bisphosphonate treatment , a diagnosis of rheumatoid arthritis , a history of hip fracture or dxa diagnosis of osteoporosis in their parents , smoking status , alcohol intake and physical activity .
calcium intake , was assessed through a spanish version of the food frequency questionnaire developed and validated by magkos et al .
dxa scans of the lumbar spine ( l1l4 ) and one hip ( usually the left ) were performed using a lunar prodigy equipment ( ge healthcare lunar , madison , wi ) .
measurements were performed by one of two technicians , both of whom were certified by the international society for clinical densitometry .
stability of the bone densitometer throughout the study ( in vitro long - term precision ) was checked through daily measurement of a spine phantom according to the manufacturer .
short - term in vivo precision was estimated by dxa scans repeated after repositioning the patient , with two measures at each site in 30 patients , according to the international society for clinical densitometry official positions 2007 .
phantom measurements showed stability of the dxa equipment throughout the study , with a coefficient of variation of 0.5% .
the combined in vivo precision for both technicians was 1.5% for the lumbar spine , 1.8% for the femoral neck , and 1.4% for the total hip .
patients were classified as normal , osteopenic , or osteoporotic according to the world health organization criteria , based on the lowest t - score at the lumbar spine , the femoral neck , or the total hip .
reference values were taken from the national health and nutrition examination survey ( nhanes iii ) , which is the recommended reference database for argentine patients .  
the ost score was calculated as 0.2 ( weight in kg  age in years ) and rounded up to the closest integer .
for example , a 64-year - old woman weighing 50  kg has an ost score of 0.2  ( 50  64 ) = 2.8 , which would be rounded up to 3 , and a 52-year - old woman weighing 67  kg has an ost score of 0.2  ( 67  52 ) = 3 . since diagnosis of osteoporosis by dxa
is based on a t - score at 2.5 or below at any of the recommended sites ( lumbar spine , femoral neck , or total hip ) , the lowest t - score was taken to dichotomously assign each result to a nonosteoporotic or osteoporotic group .
data were analyzed with the commercial statistical software prism 5.04 for windows and instat3 ( graphpad , san diego , ca ) .
the d'agostino and pearson omnibus normality test was routinely used to assess whether data departed significantly from a gaussian distribution .
if this was the case , data are presented as median ( 2575 interquartile range ) .
comparison of ost scores between women with a dxa diagnosis of osteoporosis ( t - score of 2.5 and below at any site ) and those without it was performed with mann - whitney 's test .
simple linear regression was employed to assess the relationship between ost score and the lowest t - score for each patient ( lumbar spine , femoral neck , or total hip ) .
a receiver operating characteristic ( roc ) curve was used to assess the area under the curve ( auc ) , sensitivity , and specificity .
the diagnostic odds ratio was calculated by chi - square test , and results are displayed as mean ( 95% confidence interval = ci95 ) .
the characteristics of the sample are shown in table 1 . out of 4,343 patients , a total of 2,513 women were classified as nonosteoporotic while the remainder 1,830 women were classified as osteoporotic .   among the main risk factors detected , other than advanced age or low weight , low calcium intake ( less than 1000  mg / day )
was found in 70% of women , essentially corroborating the result of a previous study in the same population .
fragility fractures were recalled in 16,5% of the patients , sedentarism in 15% , a family history of osteoporosis in 10% , long - term glucocorticoid therapy in 6.2% , and rheumatoid arthritis in 1.8% .
twelve percent of the patients were cigarette smokers at the time of the study , but high alcohol intake was reported by less than 1% . in table 2 the absolute number and the proportion of women whose t - score was at 2.5 or below at the lumbar spine , the femoral neck , the total hip , or a combination of two or all three sites are shown . of the 1,830 women with diagnosis of osteoporosis , t - scores of 2.5 or below were found in 1,207 at the lumbar spine , in 569 at the femoral neck , and in 1063 at the total hip .
these figures correspond to the total number of patients with t - scores at 2.5 or below at each site .
for example , the figure of 1,207 for the lumbar spine includes 557 women with t - score at 2.5 or below at the lumbar spine only , plus 125 women with t - score at 2.5 or below at both lumbar spine and femoral neck , plus 266 women with t - score at 2.5 or below at both lumbar spine and total hip plus 259 women with t - score at 2.5 or below at lumbar spine , femoral neck and total hip . for the whole group , ost scores ranged from 11 to + 15 ( 11 to 7 in osteoporotic and 7 to 15 in nonosteoporotic women ) .
women with a diagnosis of osteoporosis had significantly lower ost scores than those without it .
median ost scores were , respectively , 0.0 ( 2 to + 2 ) versus 2.0 ( 0.0 to 4.0 ) ; p < 0.0001 .   the result of the roc analysis is shown in figure 1 .
table 3 displays sensitivity and specificity for cut - off values from 3 to 3 . for an ost score
cut - off value of 2 , the positive predictive value was 52% and the negative predictive value was 79% in the present sample .  

figure 2 displays ost scores versus lowest t - scores for the entire sample , showing a significant linear relationship between ost scores and lowest t - scores ( p < 0.0001 ) .
if women with an ost score of 2 or lower are considered at high risk , and those above 2 are deemed at low risk , the unadjusted odds ratio for a diagnosis of osteoporosis by dxa of the high risk group versus the low risk group is 4.06 ( ci95 3.51 to 4.71 ) .  
the auc obtained from a roc analysis can range ( expressed as a percentage ) from 0 to 100 , with 50 being the line of identity . since sensitivity and specificity are both independent of disease prevalence , the same applies to the auc .
auc at or above 70% are deemed acceptable for a screening test . in the present study ,
the sensitivity and specificity of any given test vary inversely according to the chosen cut - off value . in previous reports , reviewed by rud et al .
, the sensitivity of the ost for prediction of t - scores at 2.5 or below for any region ( lumbar spine , femoral neck , or total hip ) has a median of 86% ( range of 53% to 95% ) in white women and 82% ( range 79% to 82% ) in asian women . in the present study , using a cut - off value of 2 , the sensitivity in argentinian women was 83.7% , which is intermediate between the medians for white and asian women . on the other hand ,
the specificity of the ost for any site has a median of 40% ( range 34% to 72% ) for white women but a higher median , of 64% ( range 60% to 78% ) , for asian women .
the estimated specificity in the present study with a cut - off at 2 was 44% , closer to the specificity for white women than for asian women .  
the reason why values of sensitivity and particularly the specificity for argentinian women were between those for white and asian women is not clear , but it may be related to the fact that about 80% of the argentine population has european ancestry , with minor but significant contributions from other ethnic groups .  
one limitation of this study concerns whether the sample is representative of mendoza 's postmenopausal women .
participants referred by their physicians for bmd measurement might have more risk factors than postmenopausal women in the general population . in a recent prospective study of 720 postmenopausal women undergoing their first dxa scan ,
of those below that age , 55% had at least one risk factor ( f. d. sarav , unpublished data ) .  
another reason why the sample may not accurately depict the general population of postmenopausal women of great mendoza is socioeconomic status and educational level .
recent estimates place the fraction of the population below the poverty line at about 10% for argentine urban areas .
additionally , according to official statistics , 37% of the population does not have health insurance .
although poor women or those without health insurance can still get a dxa scan through agreements between our center and the public hospital system , in practice their access is limited .
these women may differ from the ones included in the present study on their educational level , nutrition , lifestyle , and prevalence of osteoporosis .  
most of them consider additional factors other than age and weight , for example , the abone ( age , bulk , no estrogen ) ; the osteoporosis risk assessment instrument ( orai ) , which incorporates age range , body weight ( dichotomously ) , and estrogen therapy ; the simple calculated osteoporosis risk estimation ( score ) , which includes race other than black , rheumatoid arthritis , nontraumatic fractures , age , weight , and estrogen therapy ; and the osteoporosis index of risk ( osiris ) , which takes into account body weight , age , history of nontraumatic fractures , and estrogen therapy .  
.   found that ost predicted bone mass equally well than orai and score in women from the united states and the netherlands .
similarly , a comparison performed in a large sample of belgian women found that ost  performed as well as the more complex risk assessment indices ( score , orai , and osiris ) in identifying women at low risk of osteoporosis  . in a 2004 review article , wehren and siris also stated that ost ,  the simplest of the instruments , performs as well as more complex tools  .
essentially the same was found in a study of 986 postmenopausal moroccan women . in a study of canadian women ,
the performance of ost was as good as that of orai . in a systematic review
, it is stated that ost shows higher accuracy than orai and score concerning the  any region 
the authors noted , however , that overall  accuracy is similar in white women , albeit the trade - off between sensitivity and specificity may differ between ost and comparator cdrs 
( clinical decision rules ) . a very recent publication compared ost , orai , and abone and reported that ost performed best in us white women . in the american college of preventive medicine position statement on screening for osteoporosis it is stated about the ost , 
the simplicity of this screening tool and its validation in both genders and in various races account for its popularity and widespread use in selecting patients for confirmatory bmd testing  .
in the studied sample of postmenopausal women from mendoza , argentina , the ost showed a performance comparable to that reported for european and us white women .
the overall performance of the ost was adequate for a clinical screening method simple enough to be used both by patients and physicians .
of course , its use does not preclude careful consideration of other clinical risk factors for osteoporosis .
 the osteoporosis self - assessment tool ( ost ) is a clinical instrument designed to select patients at risk of osteoporosis , who would benefit from a bone mineral density measurement . 
 the ost only takes into account the age and weight of the subject . 
 it was developed for asian women and later validated for european and north american white women . 
 the performance of the ost in a sample of 4343 women from greater mendoza , a large metropolitan area of argentina , was assessed . 
 dual x - ray absorptiometry ( dxa ) scans of lumbar spine and hip were obtained . 
 patients were classified as either osteoporotic ( n = 1830 ) or nonosteoporotic ( n = 2513 ) according to their lowest t - score at any site . 
 osteoporotic patients had lower ost scores ( p < 0.0001 ) . 
 a receiver operating characteristic ( roc ) curve showed an area under the curve of 71% ( p < 0.0001 ) , with a sensitivity of 83.7% and a specificity of 44% for a cut - off value of 2 . 
 positive predictive value was 52% and negative predictive value was 79% . 
 the odds ratio for the diagnosis of osteoporosis was 4.06 ( ci95 3.51 to 4.71 ; p < 0.0001 ) . 
 it is concluded that the ost is useful for selecting postmenopausal women for dxa testing in the studied population . 