Background: Preterm infants are at risk of impaired bone health in later life. Dual-energy X-ray absorptiometry-scan (DXA) is the gold standard to determine bone mineralization. Phalangeal quantitative ultrasound (pQUS) is an alternative technique that is inexpensive, easy to use and radiation-free. The aim of this study was to investigate whether both techniques reveal equivalent results.
Materials and methods: Sixty former preterm infants (31 boys; 29 girls) received a DXA and pQUS at age 9 to 10 years. DXA measured bone mineral content (BMC) and bone mineral density (BMD) for total body and lumbar spine (L1-4), while pQUS measured the amplitude dependent speed of sound (AD-SoS) and bone transit time (BTT) at metacarpals II-IV providing continuous values and Z-scores based on age and sex. Four statistical methods evaluated the association between both techniques: Pearson's correlation coefficients, partial correlation coefficients adjusted for gestational age, height and BMI, Bland-Altman analysis and cross tabulation.
Results: Both techniques showed a statistically significant weak correlation for continuous values as well as Z-scores (0.291-0.462, p < 0.05). Boys had significant and relatively high correlations (0.468-0.585, p < 0.05). In comparison, the correlations for girls were not significant. Correlation coefficients further decreased while calculating the partial correlations. The Bland-Altman plots showed poor agreement. Sensitivity ranged from 33% to 92% and specificity from 16% to 68%. Positive and negative predictive values ranged from 4% to 38% and 82% to 97%, respectively.
Conclusions: We found statistically significant weak correlations and poor agreement between DXA and pQUS measurements. DXA is not equivalent to pQUS and therefore not replaceable by this technique in former preterm born children at the age of 9 to 10 years.
Keywords: AD-SoS, amplitude dependent speed of sound; BMC, bone mineral content; BMD, bone mineral density; BTT, bone transit time; Bone development; Children; Correlation; DXA, dual-energy X-ray absorptiometry-scan; Dual-energy X-ray absorptiometry-scan; ISCD, International Society of Clinical Densitometry; QUS, quantitative ultrasound; SOS, speed of sound; Speed of sound; Ultrasound; pQUS, phalangeal quantitative ultrasound.