THE EFFECTS OF STANDARDIZATION AND REFERENCE VALUES ON PATIENT CLASSIFICATION FOR SPINE AND FEMUR DUAL-ENERGY X-RAY ABSORPTIOMETRY

The effect of two methods for standardizing dual-energy X-ray absorpti ometry (DXA) measurements on patient classification by the T-score has been determined for a group of over 2000 patients. The methods propos ed by the international DXA Standardization Committee and the European Community's COMAC-BME group were used in conjunction with young refer ence data from the major DXA manufacturers, the COMAC-BME group and th e third US National Health and Nutrition Examination Survey (NHANES II I). The two standardization techniques produced dissimilar classificat ions as measured by the kappa statistic (kappa = 0.34-0.90), especiall y for the femoral neck, with up to 24.3% of patients reclassified from osteopenic to normal and 18.6% reclassified from osteoporotic to oste openic when the standardization method was changed, Considering the ef fects of both reference data and standardization techniques together, there was a wide variation of patient classification, with the number of patients classified as osteoporotic varying from 9.6% to 21.1% for the postero-anterior spine L2-4 region and from 2.3% to 27.6% for the femoral neck, The agreement between different classifications ranged w idely. from very poor to excellent (kappa = 0.02-0.98). The creation o f standardized reference data must be an important priority in order t o harmonize patient management using standardized BMD measurements. Th e choice of standardization technique, however, must be addressed in l ight of the results presented here.