DUAL-ENERGY X-RAY ABSORPTIOMETRY NORMAL REFERENCE RANGE USE WITHIN THE UK AND THE EFFECT OF DIFFERENT NORMAL RANGES ON THE ASSESSMENT OF BONE-DENSITY

The number of different normal ranges used on dual energy X-ray absorp tiometry (DEXA) machines in the United Kingdom was determined by means of a postal questionnaire. Both femoral neck and posteroanterior spin e L2-L4 regions were considered. It was clear from this survey that a variety of normal ranges were in use for all manufacturers of DEXA sys tems. The effects of four normal ranges supplied by Norland for use wi thin the UK on the stratification of over 1000 consecutive patients in to different grades of bone mineral density (BMD) and Z-score were exa mined. The main outcomes measure the number of patients with BMD less than 80% of mean age-matched BMD and Z-score less than -1.5 over the f emoral neck and spine for each normal range. The percentage of patient s for each normal range with BMD less than 80% of mean for the femoral neck were 24.6%, 7.4%, 17.5% and 11.1% and for the spine 12.1%, 7.4%: 16.5% and 14.4%, respectively. For the femoral neck, 21.2%, 5.0%, 12. 9% and 12.1% of patients had Z-scores of less than -1.5: for the spine this was 7.9%, 8.1%, 14.2% and 13.6% of patients. These differences b etween ranges are large enough to influence patient management-patient s may be diagnosed as osteoporotic using one range and normal using an other. The relationship between hip and spine measurements was also st udied as some therapeutic agents do not affect BMD equally at all anat omical sites. The number of patients with a lower hip than spine BMD g rade varied from 12.3% to 34.4%, and with a lower hip than spine Z-sco re from 14.0% to 43.4%. Choice of normal range thus has a critical eff ect on the categorization of osteoporotic patients using DEXA. The wid e variety of normal ranges indicates that there are likely to be diffe rences in patient management throughout the country. This will be an i ncreasing problem due to the ability of NHS purchasers to switch contr acts from one provider to another.