The impact of hip subregion reference data on osteoporosis diagnosis.

Manufacturers of bone densitometry devices have been moving from manufacturer-specific reference values to data derived from larger population-based cohorts such as the National Health and Nutrition Evaluation Survey (NHANES) III. One bone densitometer manufacturer has released software that provides hip subregion T-score calculations based upon four slightly different versions of hip reference data. Our aim was to determine how changes in hip reference data affect diagnostic classification based on minimum T-scores in older women. We extracted results for lumbar spine and hip bone density measurements from the Manitoba Bone Density database for women aged 50 years or older who had baseline scans on the manufacturer's equipment (n=17,053). T-scores were calculated using manufacturer-specific non-NHANES data and three software implementations of NHANES reference data. One software version gave results at subregions of the hip that were significantly lower than with the three other sets of reference data from the same manufacturer (mean femoral neck T-score absolute difference 0.23-0.48, P<0.00001; mean trochanter T-score absolute difference 0.49-0.70, P<0.00001). As a result the proportion of measurements with a T-score of -2.5 or lower almost doubled at the femoral neck (14.3 versus 27.7%, P<0.00001) and approximately tripled at the trochanter (8.1 versus 24.0%, P<0.00001). The final patient classification of osteoporosis based on a minimum T-score of -2.5 or lower from all four measured sites differed significantly between the four versions (absolute difference 7.9 to 10.4%, P<0.00001). Small changes in the reference data used in T-score calculations had large effects on patient categorization and the calculated prevalence of osteoporosis. The impact of changes in reference data need to be carefully evaluated by users and manufacturers before widespread clinical dissemination.