A SURVEY OF DUAL-ENERGY X-RAY ABSORPTIOMETRY (DEXA) NORMAL REFERENCE RANGES USED WITHIN THE UK AND THEIR EFFECT ON PATIENT CLASSIFICATION

Differences between dual-energy X-ray absorptiometry (DEXA) normal ran ges can lead to patients being characterized as osteoporotic using one range and normal using another. To investigate the diversity of norma l ranges used within the UK, a survey of all DEXA sites was carried ou t with a 60.6% response rate. The effect of the different ranges was e valuated by translating each range to an equivalent range for a Norlan d XR-26 system and applying the ranges to stratify a representative sa mple of over 1000 patients into grades of bone density based on percen tages of age-matched mean BMD, Z-scores and T-scores. The effect of fe moral neck and P/A spine L2-L4 regions was considered both separately and jointly. Large differences between the normal ranges were apparent , which resulted in the classification of the number of patients with a Z-score of less than -2.0 varying by a factor of more than 20 for th e femoral neck and more than 3 for the spine. The number of patients d efined as osteoporotic by a T-score less than -2.5 varied from none to over one-third of patients for the hip and by a factor of almost 3 fo r the spine. The exclusion criteria used for construction of the norma l ranges varied markedly with none constructed using population-based sampling. Smoothing of normal ranges was carried out by DEXA manufactu rers, while local normal ranges made use of raw unprocessed data. Ther e is reason to question the validity of such processing. We recommend the construction of a unified UK normal range applicable to all UK DEX A systems in order to harmonize patient management and care.