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Dual energy x-ray absorptiometry and quantitative ultrasound are not interchangeable in diagnosing abnormal bones
  1. J E Williams1,
  2. C M Wilson2,
  3. L Biassoni2,
  4. R Suri3,4,
  5. M S Fewtrell1
  1. 1Childhood Nutrition Research Centre, UCL Institute of Child Health, London, UK
  2. 2Radiology Department, Great Ormond Street Hospital for Children NHS Trust, London, UK
  3. 3Respiratory Unit, Great Ormond Street Hospital for Children NHS Trust, London, UK
  4. 4Portex Unit, UCL Institute of Child Health, London, UK
  1. Correspondence to Jane Williams, Childhood Nutrition Research Centre, UCL Institute of Child Health, 30 Guilford St, London WC1N 1EH, UK; jane.williams{at}ucl.ac.uk

Abstract

Objective To evaluate whether dual energy x-ray absorptiometry (DXA) and quantitative ultrasound (QUS) classify the same children as ‘abnormal’ (SD (z) score (SDS) ≤−2).

Methods Speed of sound (SOS) was measured at the radius and tibia using QUS and lumbar spine bone mineral density (BMD) using DXA in 621 subjects aged 5–20 years; healthy 412, cystic fibrosis 117 and obese 92.

Results BMD SDS positively (p<0.001) and tibia SOS SDS negatively correlated with size (p<0.05). Disagreement between DXA and QUS for ‘abnormal’ scans occurred in 6–31%. Those with abnormal BMD and normal SOS SDS had lower mean BMI SDS than those with normal BMD and abnormal SOS SDS. SOS measurements were unobtainable in some children, especially in the obese group.

Conclusions DXA and QUS identify different individuals as ‘abnormal’. Agreement between BMD and tibia SOS is lower in obese subjects. Without a gold-standard, it is difficult to determine which technique is more ‘correct’.

https://doi.org/10.1136/archdischild-2011-301326

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    Footnotes

    • Funding This study was funded from the core funds of the Childhood Nutrition Research Centre.

    • Competing interests None.

    • Ethics approval The ethics committee of The Institute of Child Health and Great Ormond St Hospital.

    • Provenance and peer review Not commissioned; externally peer reviewed.