Accounting for body size deviations when reporting bone mineral density variables in children.
In a child, bone mineral density (BMD) may differ from an age-expected normal value, not only because of the presence of disease, but also because of deviations of height or weight from population averages. Appropriate adjustment for body size deviations simplifies interpretation of BMD measurements.


BACKGROUND
For children, a bone mineral density (BMD) measurement is normally expressed as a Z score. Interpretation is complicated when weight or height distinctly differ from age-matched children. We develop a procedure to allow for the influence of body size deviations upon measured BMD.


METHODS
We examined the relation between body size deviation and spine, hip and whole body BMD deviation in 179 normal children (91 girls). Expressions were developed that allowed derivation of an expected BMD based on age, gender and body size deviation. The difference between measured and expected BMD was expressed as a HAW score (Height-, Age-, Weight-adjusted score).


RESULTS
In a second independent sample of 26 normal children (14 girls), measured spine, total femur and whole body BMD all fell within the same single normal range after accounting for age, gender and body size deviations. When traditional Z scores and HAW scores were compared in 154 children, 17.5% showed differences of more than 1 unit and such differences were associated with height and weight deviations.


CONCLUSIONS
For almost 1 in 5 children, body size deviations influence BMD to an extent that could alter clinical management.
Department of Nuclear Medicine, Hamilton Health Sciences, Hamilton, ON, Canada, L8N 3Z5. webber@hhsc.ca
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Webber
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Sala
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Barr
D015502:Absorptiometry, Photon; D001827:Body Height; D049628:Body Size; D001835:Body Weight; D015519:Bone Density; D001842:Bone and Bones / Q000502:physiology*; D002648:Child; D002675:Child, Preschool; D005260:Female; D005269:Femur / Q000502:physiology; D006801:Humans; D008159:Lumbar Vertebrae / Q000502:physiology; D008297:Male; D011446:Prospective Studies; D012016:Reference Values; D012189:Retrospective Studies