DUAL-ENERGY X-RAY ABSORPTIOMETRY FOR MEASURING TOTAL BONE-MINERAL CONTENT IN THE RAT - STUDY OF ACCURACY AND PRECISION

Sequential studies of osteopenic bone disease in small animals require the availability of non-invasive, accurate and precise methods to ass ess bone mineral content (BMC) and bone mineral density (BMD). Dual-en ergy X-ray absorptiometry (DXA), which is currently used in humans for this purpose, can also be applied to small animals by means of adapte d software. Precision and accuracy of DXA was evaluated in 10 rats wei ghing 50-265 g. The rats were anesthetized with a mixture of ketamine- xylazine administrated intraperitoneally. Each rat was scanned six tim es consecutively in the antero-posterior incidence after repositioning using the rt whole-body software for determination of whole-body BMC and BMD (Hologic QDR 1000(R), software version 5.52). Scan duration wa s 10-20 min depending on rat size. After the last measurement, rats we re sacrificed and soft tissues were removed by dermestid beetles. Skel etons were then scanned in vitro (ultra high resolution software, vers ion 4.47). Bones were subsequently ashed and dissolved in hydrochloric acid and total body calcium directly assayed by atomic absorption spe ctrophotometry (TBCa[chem]). Total body calcium was also calculated fr om the DXA whole-body in vivo measurement (TBCa [DXA]) and from the ul tra high resolution measurement (TBCa[UH]) under the assumption that c alcium accounts for 40.5% of the BMC expressed as hydroxyapatite. Prec ision error for whole-body BMC and BMD (mean +/- S.D.) was 1.3% and 1. 5%, respectively. Simple regression analysis between TBCa[DXA] or TBCa [UH] and TBCa[chem] revealed tight correlations (n = 0.991 and 0.996, respectively), with slopes and intercepts which were significantly dif ferent from 1 and 0, respectively. Mean accuracy error for TBCa[DXA] w as 8.5% for all rats and 5.7% after excluding the 50-g rats. It was 6. 4% for TBCa[UH] (all rats). We conclude that whole-body DXA provides h ighly precise and reasonably accurate estimates of skeletal calcium co ntent in the rat in vivo.