Background: Quantitative ultrasound (QUS) is a quick, non-invasive and inexpensive method to measure bone strength. Moreover, the device is portable, which makes it easy to be used in the field. In contrast to other bone measuring techniques, QUS does not use any ionised radiation. However, the validity of QUS in the measurement of bone health and the relationship between QUS output and body composition have not been assessed in very young children. Objective: To investigate the relationship between paediatric calcaneal QUS and both dual-energy X-ray absorptiometry (DXA) and calcaneal DXA with laser (DXL) and body composition parameters. Subjects: A total of 37 Belgian children (10 boys and 27 girls; 4 to 8 years old) underwent a calcaneal QUS as well as a DXA scan. A total of 24 Swedish children (15 boys and 9 girls; 3 to 5 years old) underwent a calcaneal QUS as well as a heel DXL scan. The height and weight of all children were measured. Results: The QUS stiffness index (SI) was significantly negatively correlated with bone mineral density (BMD) of the total body (r ¼ À0.370, P ¼ 0.02). No significant correlations were found between the SI and DXL results. In the total sample, the SI showed a significant positive correlation with body mass index (BMI) (r ¼ 0.298, P ¼ 0.02), even after correction for age, gender and centre. In the Belgian sample, the SI was also significantly positively correlated with total body fat mass content (r ¼ 0.416, P ¼ 0.01) and body fat percentage (r ¼ 0.566, Po0.01) obtained by whole-body DXA. Conclusion: The SI measured by QUS does not correlate significantly with BMD values measured by DXA or DXL in 3-to 8-year-old children. However, there is a significant positive correlation between SI and BMI and body fat %.

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