Intermachine differences in DXA measurements vary by skeletal site, and impact the assessment of low bone density in children.

Bone mineral content (BMC) and areal-bone mineral density (aBMD) measurements of the lumbar spine (LS) and whole body less head (WBLH) by dual energy X-ray absorptiometry (DXA) are recommended for bone health assessment in children. Intermachine differences were not considered previously in formulating these recommendations. DXA measurements of the LS, WBLH, total hip, femoral neck and distal 1/3 radius from the Bone Mineral Density in Childhood Study were examined. Healthy children, ages 6 to 16 years, from five clinical centers participated. The same spine, whole body, and femur phantoms were measured on each Center's DXA machine. Percentage of individuals with low BMC or aBMD (Z-score < -1.5) was determined. Clinical center differences were evaluated by analysis of covariance adjusting for height and BMI Z-score, calcium intake, physical activity, Tanner stage and bone age. Logistic regression assessed odds of low BMC or aBMD across clinical centers. Significant differences among Clinical Centers (p < 0.05) were evident in adjusted mean BMC and aBMD Z-scores (n = 1503) for all skeletal sites. WBLH BMC and aBMD Z-scores had the greatest range across centers (-0.13 to 0.24, and -0.17 to 0.56, respectively). The percentage of children with Z-scores less than -1.5 varied among Clinical Centers from 1.9 [95%CI 0.8, 4.5] to 8.1 [95%CI 5.7, 11.3] for WBLH BMC, 1.1 [95%CI 0.4, 3.5] to 6.3 [95%CI 3.8, 10.1] for WBLH aBMD, and from 4.4 [95%CI 2.8, 7.0] to 12.6 [95%CI 9.3, 16.9] for distal 1/3 radius aBMD. For each skeletal site except total hip aBMD and femoral neck BMC, at least one center had significantly lower odds of low bone density. By design, our reference ranges capture intermachine variability. Most clinical centers don't know where their machine falls within the range of intermachine variability, and this may affect diagnosis of children evaluated for conditions that threaten bone health. Total hip scans showed the least, and whole body scans showed the most intermachine variability. Pediatric bone health assessment recommendations should recognize intermachine differences and address this important issue.

Zemel BS ，Wasserman H ，Kelly A ，Fan B ，Shepherd J ，Lappe J ，Gilsanz V ，Oberfield S ，Winer KK ，Kalkwarf HJ ... -  《-》

Reference Ranges for Bone Mineral Content and Density by Dual Energy X-Ray Absorptiometry for Young Children.

Assessment of bone health in young children has been hampered by limited reference values for bone mineral content (BMC) and areal bone mineral density (aBMD) by dual energy X-ray absorptiometry (DXA). To identify age, sex, and population ancestry effects on BMC and aBMD and develop smoothed reference ranges for BMC and aBMD in young children. To quantify precision of bone measurements and influence of height-for-age Z-scores on bone Z-scores. We recruited 484 healthy children ages 1 to 2 years or 4.5 to 5 years at 2 clinical centers, who were seen once or up to 7 times over a 3-year period. Lumbar spine, distal forearm, and whole-body subtotal (ages ≥ 3 years) BMC and aBMD were measured by DXA. These data were combined with data from the Bone Mineral Density in Childhood Study from children ages 5 to 8.9 years to create the smoothed reference curves. For 1- to 5-year-olds, BMC and aBMD at all skeletal sites increased with age. Age trends differed by sex for BMC and aBMD of the spine, distal one-third radius, ultradistal radius, and by ancestry (Black vs non-Black) for all measures. BMC and aBMD precision (% coefficient of variation) ranged from 1.0% to 4.4%. Height Z-scores were positively associated with bone Z-scores and accounted for 4% to 45% of the variance. We demonstrate the feasibility of bone density measurements in young children and provide robust reference ranges and stature adjustments for calculation of bone Z-scores at multiple skeletal sites to enable bone health assessments.

Kalkwarf HJ ，Shepherd JA ，Fan B ，Sahay RD ，Ittenbach RF ，Kelly A ，Yolton K ，Zemel BS ... -  《-》

Changes in pediatric DXA measures of musculoskeletal outcomes and correlation with quantitative CT following treatment of acute lymphoblastic leukemia.

We previously reported significant gains in pQCT measures of tibia trabecular bone mineral density (BMD) and cortical structure following completion of therapy in children and adolescents with acute lymphoblastic leukemia (ALL). The objective of this study was to examine changes in DXA measures used in clinical practice and expressed as Z-scores using robust national reference data. Children and adolescents, ages 5 to 18 years were enrolled within 2 (median 0.8) years of completing ALL therapy. DXA total-body less-head bone mineral content (TBLH-BMC), and spine, total hip, femoral neck, and 1/3rd radius areal BMD (aBMD) were assessed in 45 participants at enrollment and 12-months later. Linear regression models examined correlates of changes in DXA Z-scores. Changes in DXA outcomes were compared to changes in tibia pQCT trabecular and cortical volumetric BMD (vBMD) and cortical area. At enrollment, DXA TBLH-BMC, spine and radius aBMD Z-scores were not significantly reduced in ALL survivors; however, total hip [median -0.74 (IQ range -1.51 to -0.04)] and femoral neck [-0.51 (-1.24 to 0.14)] aBMD Z-scores were lower (both p < 0.01) compared to reference data. DXA Z-scores at all skeletal sites increased over 12 months. Despite improvement, total hip Z-score remained lower at -0.55 (-1.05 to 0.18). The increases in TBLH-BMC, total hip and femoral neck aBMD Z-scores were more pronounced in those enrolled within 6 months of completing ALL therapy, compared to those enrolled at >6 months. Gains in TBLH-BMC, total hip, femoral neck and radius aBMD Z-scores were significantly associated with gains in tibia cortical area Z-scores (R = 0.56 to 0.67, p ≤ 0.001). Changes in TBLH and proximal femur sites were associated with gains in trabecular vBMD Z-scores (R = 0.37 to 0.40; p ≤ 0.01); these associations were not significant when adjusted for gains in cortical area. In summary, gains in DXA measures were most pronounced in total hip and femoral neck following ALL therapy. The gains in all DXA measures, with the exception of lumbar spine, reflected gains in cortical area. Overall, ALL survivors demonstrate skeletal recovery following completion of therapy; a small sub-group continue to demonstrate deficits and benefit from continued observation to ensure improvement over time.

Mostoufi-Moab S ，Kelly A ，Mitchell JA ，Baker J ，Zemel BS ，Brodsky J ，Long J ，Leonard MB ... -  《-》

Pediatric Bone Mineral Accrual Z-Score Calculation Equations and Their Application in Childhood Disease.

Annual gains in BMC and areal bone mineral density (aBMD) in children vary with age, pubertal status, height-velocity, and lean body mass accrual (LBM velocity). Evaluating bone accrual in children with bone health-threatening conditions requires consideration of these determinants. The objective of this study was to develop prediction equations for calculating BMC/aBMD velocity SD scores (velocity-Z) and to evaluate bone accrual in youth with health conditions. Bone and body compositions via DXA were obtained for up to six annual intervals in healthy youth (n = 2014) enrolled in the Bone Mineral Density in Childhood Study (BMDCS) . Longitudinal statistical methods were used to develop sex- and pubertal-status-specific reference equations for calculating velocity-Z for total body less head-BMC and lumbar spine (LS), total hip (TotHip), femoral neck, and 1/3-radius aBMD. Equations accounted for (1) height velocity, (2) height velocity and weight velocity, or (3) height velocity and LBM velocity. These equations were then applied to observational, single-center, 12-month longitudinal data from youth with cystic fibrosis (CF; n = 65), acute lymphoblastic leukemia (ALL) survivors (n = 45), or Crohn disease (CD) initiating infliximab (n = 72). Associations between BMC/aBMD-Z change (conventional pediatric bone health monitoring method) and BMC/aBMD velocity-Z were assessed. The BMC/aBMD velocity-Z for CF, ALL, and CD was compared with BMDCS. Annual changes in the BMC/aBMD-Z and the BMC/aBMD velocity-Z were strongly correlated, but not equivalent; LS aBMD-Z = 1 equated with LS aBMD velocity-Z = -3. In CF, BMC/aBMD velocity-Z was normal. In posttherapy ALL, BMC/aBMD velocity-Z was increased, particularly at TotHip (1.01 [-.047; 1.7], p < 0.0001). In CD, BMC/aBMD velocity-Z was increased at all skeletal sites. LBM-velocity adjustment attenuated these increases (eg, TotHip aBMD velocity-Z: 1.13 [0.004; 2.34] versus 1.52 [0.3; 2.85], p < 0.0001). Methods for quantifying the BMC/aBMD velocity that account for maturation and body composition changes provide a framework for evaluating childhood bone accretion and may provide insight into mechanisms contributing to altered accrual in chronic childhood conditions. © 2018 American Society for Bone and Mineral Research.

Kelly A ，Shults J ，Mostoufi-Moab S ，McCormack SE ，Stallings VA ，Schall JI ，Kalkwarf HJ ，Lappe JM ，Gilsanz V ，Oberfield SE ，Shepherd JA ，Winer KK ，Leonard MB ，Zemel BS ... -  《-》

Pediatric Reference Ranges for Ultradistal Radius Bone Density: Results from the Bone Mineral Density in Childhood Study.

The ultradistal (UD) radius is rich in trabecular bone and is easily measured by dual energy X-ray absorptiometry (DXA). UD radius areal bone mineral density (aBMD) may help identify trabecular bone deficits, but reference data are needed for research and clinical interpretation of this measure. We developed age-, sex-, and population ancestry-specific reference ranges for UD radius aBMD assessed by DXA and calculated Z-scores. We examined tracking of UD radius aBMD Z-scores over 6 years and determined associations between UD radius aBMD Z-scores and other bone measures by DXA and peripheral quantitative computed tomography. Multicenter longitudinal study. A total of 2014 (922 males, 22% African American) children ages 5 to 19 years at enrollment who participated in the Bone Mineral Density in Childhood Study. UD radius aBMD. UD radius aBMD increased nonlinearly with age (P < 0.001) and tended to be greater in males versus females (P = 0.054). Age-, sex-, and ancestry-specific UD radius aBMD reference curves were constructed. UD radius aBMD Z-scores positively associated with Z-scores at other skeletal sites (r = 0.54-0.64, all P < 0.001) and peripheral quantitative computed tomography measures of distal radius total volumetric BMD (r = 0.68, P < 0.001) and trabecular volumetric BMD (r = 0.70, P < 0.001), and was weakly associated with height Z-score (r = 0.09, P = 0.015). UD radius aBMD Z-scores tracked strongly over 6 years, regardless of pubertal stage (r = 0.66-0.69; all P < 0.05). UD radius aBMD Z-scores strongly associated with distal radius trabecular bone density, with marginal confounding by stature. These reference data may provide a valuable resource for bone health assessment in children.

Kindler JM ，Kalkwarf HJ ，Lappe JM ，Gilsanz V ，Oberfield S ，Shepherd JA ，Kelly A ，Winer KK ，Zemel BS ... -  《-》