Amalgamated Reference Data for Size-Adjusted Bone Densitometry Measurements in 3598 Children and Young Adults-the ALPHABET Study

Abstract

The increasing use of dual-energy X-ray absorptiometry (DXA) in children has led to the need for robust reference data for interpretation of scans in daily clinical practice. Such data need to be representative of the population being studied and be "future-proofed" to software and hardware upgrades. The aim was to combine all available pediatric DXA reference data from seven UK centers to create reference curves adjusted for age, sex, ethnicity, and body size to enable clinical application, using in vivo cross-calibration and making data back and forward compatible. Seven UK sites collected data on GE Lunar or Hologic Scanners between 1996 and 2012. Males and females aged 4 to 20 years were recruited (n = 3598). The split by ethnic group was white 2887; South Asian 385; black Afro-Caribbean 286; and mixed heritage 40. Scans of the total body and lumbar spine (L₁ to L₄ ) were obtained. The European Spine Phantom was used to cross-calibrate the 7 centers and 11 scanners. Reference curves were produced for L₁ to L₄ bone mineral apparent density (BMAD) and total body less head (TBLH) and L₁ to L₄ areal bone mineral density (aBMD) for GE Lunar Prodigy and iDXA (sex- and ethnic-specific) and for Hologic (sex-specific). Regression equations for TBLH BMC were produced using stepwise linear regression. Scans of 100 children were randomly selected to test backward and forward compatibility of software versions, up to version 15.0 for GE Lunar and Apex 4.1 for Hologic. For the first time, sex- and ethnic-specific reference curves for lumbar spine BMAD, aBMD, and TBLH aBMD are provided for both GE Lunar and Hologic scanners. These curves will facilitate interpretation of DXA data in children using methods recommended in ISCD guidelines. The databases have been created to allow future updates and analysis when more definitive evidence for the best method of fracture prediction in children is agreed. © 2016 American Society for Bone and Mineral Research.

Keywords: BMC; BMD; DXA; LEAN MASS; PEDIATRIC; REFERENCE.

Figure 1

Comparison of GE Lunar iDXA™ lumbar spine BMAD LMS reference curves between the three different ethnic groups. (A) BMAD (g/cm³) for girls; (B) BMAD (g/cm³) for boys. Solid black line represents the mean for White Caucasian Children (± 95% Confidence interval -dotted black line). Dark grey dashed line represents the mean for Black Afro-Caribbean Children; Dashed light grey line represents the mean for South Asian Children.

Figure 2

Comparison of lumbar spine BMAD LMS reference curves between males and females (A) GE Lunar iDXA; (B) Hologic Discovery. Solid black line represents males (mean ± 95% Confidence interval). Dashed line represents females (mean ± 95% Confidence interval).

Figure 3

Comparison of lumbar spine BMAD LMS reference curves between manufacturers, GE Lunar iDXA™ compared to Transformed Hologic Discovery (Hologic data transformed using cross calibration equations generated from the European Spine Phantom). (A) Females; (B) Males. Solid black line represents GE Lunar iDXA™ (mean ± 95% Confidence interval). Dashed line represents Hologic Discovery (mean ± 95% Confidence interval).