Assessment of dual-energy X-ray absorptiometry measures of bone health in pediatric chronic kidney disease

Abstract

Background: Dual-energy X-ray absorptiometry (DXA) techniques are limited in childhood chronic kidney disease (CKD) by the confounding effect of short stature and opposing parathyroid hormone effects on trabecular and cortical bone. Peripheral quantitative computed tomography (pQCT) is not subject to these limitations.

Methods: Lumbar spine (LS) and whole-body (WB) DXA and tibia pQCT scans were obtained in 88 stage 4-5 CKD and >650 healthy participants, ages 5-21 years. Sex- and race-specific Z-scores were generated for bone mineral density (BMD) and bone mineral content (BMC) by DXA, relative to age and adjusted for height Z-score (LS-BMD-Z and WB-BMC-Z), and compared to pQCT Z-scores for trabecular BMD (TrabBMD-Z) for age and cortical BMC (CortBMC-Z) for age and tibia length.

Results: LS-BMD-Z [0.50 (95% C.I. 0.28, 0.73), p<0.0001] and TrabBMD-Z [0.53 (0.27, 0.79), p<0.0001] were greater in CKD, and WB-BMC-Z [-0.36 (-0.53, -0.19), p<0.0001] and CortBMC-Z [-0.48 (-0.70, -0.27), p<0.0001] were lower, compared to reference participants. Z-scores were correlated at trabecular (LS-BMD-Z and TrabBMD-Z: R=0.36) and cortical (WB-BMC-Z and CortBMC-Z: R=0.64) sites in CKD; similar to correlations in reference participants.

Conclusions: Lumbar spine and whole-body DXA suggested greater trabecular BMD and lower cortical BMC in CKD, consistent with pQCT results; however, correlations were modest. Studies are needed to identify methods that predict fracture in childhood CKD.

Fig. 1

Height Z-score and DXA Z-scores relative to age in CKD participants. a WB BMC_ageZ-scores significantly increased as height Z-score category increased. b LS BMD_ageZ-scores also significantly increased with height Z-score category. Abbreviations: DXA – dual-energy X-ray absorptiometry; CKD – chronic kidney disease; WB BMC_ageZ – DXA whole body less head bone mineral content Z-score for age; LS BMD_ageZ – DXA lumbar spine bone mineral density Z-score for age

Fig. 2

Tibia pQCT Z-scores and DXA Z-scores in CKD participants. a Tibia CortBMC-Z, WB BMC_ageZ, and WB BMC_htZZ were significantly lower and WB BMC_htZ was no different in CKD participants, compared to the reference participants. b Tibia TrabBMD-Z and LS BMD_htZZ were significantly greater and LS BMD_ageZ was no different in CKD participants, compared to the reference participants. Abbreviations: pQCT – peripheral quantitative computed tomography; DXA – dual-energy X-ray absorptiometry; CKD – chronic kidney disease; Tibia CortBMC-Z – pQCT tibia cortical bone mineral content Z-score for age and tibia length; WB BMC_ageZ – DXA whole body less head bone mineral content Z-score for age; WB BMC_htZ – DXA whole body less head bone mineral content Z-score for height; WB BMC_htZZ – DXA whole body less head bone mineral content Z-score for age, adjusted for height Z-score; Tibia TrabBMD-Z – pQCT tibia trabecular bone mineral density Z-score for age; LS BMD_ageZ – DXA lumbar spine bone mineral density Z-score for age; LS BMD_htZZ – DXA lumbar spine bone mineral density Z-score for age, adjusted for height Z-score

Fig. 3

Association of tibia pQCT TrabBMD-Z and LS DXA Z-scores with age in CKD participants. a There was a negative association between age and tibia TrabBMD-Z. Greater tibia TrabBMD-Z-scores were seen in younger children with CKD and TrabBMD-Z-scores were decreased in older children with CKD. b, c There was a lack of association of age with LS BMD_ageZ and LS BMD_htZZ. LS BMD_htZZ-scores remained elevated even in older children. Abbreviations: pQCT – peripheral quantitative computed tomography; DXA – dual-energy X-ray absorptiometry; CKD – chronic kidney disease; Tibia TrabBMD-Z – pQCT tibia trabecular bone mineral density Z-score for age; LS BMD_ageZ – DXA lumbar spine bone mineral density Z-score for age; LS BMD_htZZ – DXA lumbar spine bone mineral density Z-score for age, adjusted for height Z-score