Lumbar spine bone measurements in infants: whole-body vs lumbar spine dual X-ray absorptiometry scans.

Availability of software delineation of the lumbar spine region from infant whole-body (IWB) dual energy X-ray absorptiometry scan offers an opportunity to gain additional information at the lumbar spine without a separate scan, although the validity of this technique has never been tested. Lumbar spine measurements derived from IWB scans using software-delineated first to fourth lumbar vertebrae, and from specific infant spine (IS) scans, were determined in 111 infants using two pencil-beam densitometers. Intraoperator repeatability determined by reanalysis of 10 pairs of IWB and IS scans from each densitometer. Lumbar spine area, bone mineral content, and bone mineral density from IWB and IS scans were significantly correlated r = 0.68-0.95, p < 0.001 for all comparisons) but show poor agreement (Bland-Altman method) with one SD of the differences equal to 26-55% of the mean. Intraoperator reanalysis shows good agreement with one SD of the differences from IWB scans at <7% of the mean, and <2.9% from IS scans. Findings were the same for both densitometers. We conclude that lumbar spine bone measurements from IWB or IS scans are highly reproducible and significantly correlated but data from IWB scans cannot substitute for data from IS scans.