Mineral and bone disorder (MBD) is widely prevalent in children with chronic kidney disease (CKD) and is associated with significant morbidity. CKD may cause disturbances in bone remodelling/modelling, which are more pronounced in the growing skeleton, manifesting as short stature, bone pain and deformities, fractures, slipped epiphyses and ectopic calcifications. Although assessment of bone health is a key element in the clinical care of children with CKD, it remains a major challenge for physicians. On the one hand, bone biopsy with histomorphometry is the gold standard for assessing bone health, but it is expensive, invasive and requires expertise in the interpretation of bone histology. On the other hand, currently available non-invasive measures, including dual-energy X-ray absorptiometry and biomarkers of bone formation/resorption, are affected by growth and pubertal status and have limited sensitivity and specificity in predicting changes in bone turnover and mineralization. In the absence of high-quality evidence, there are wide variations in clinical practice in the diagnosis and management of CKD-MBD in childhood. We present clinical practice points (CPPs) on the assessment of bone disease in children with CKD Stages 2–5 and on dialysis based on the best available evidence and consensus of experts from the CKD-MBD and Dialysis working groups of the European Society for Paediatric Nephrology and the CKD-MBD working group of the European Renal Association–European Dialysis and Transplant Association. These CPPs should be carefully considered by treating physicians and adapted to individual patients’ needs as appropriate. Further areas for research are suggested.

Serum calcium (Ca), bone biomarkers, and radiological imaging do not allow accurate evaluation of bone mineral balance (BMB), a key determinant of bone mineral density (BMD) and fracture risk. We studied naturally occurring stable (non-radioactive) Ca isotopes in different body pools as a potential biomarker of BMB. 42 Ca and 44 Ca are absorbed from our diet and sequestered into different body compartments following kinetic principles of isotope fractionation; isotopically light 42 Ca is preferentially incorporated into bone, whereas heavier 44 Ca preferentially remains in blood and is excreted in urine and feces. Their ratio (δ 44/42 Ca) in serum and urine increases during bone formation and decreases with bone resorption. In 117 healthy participants, we measured Ca isotopes, biomarkers, and BMD by dual-energy X-ray absorptiometry (DXA) and tibial peripheral quantitative CT (pQCT). 44 Ca and 42 Ca were measured by multi-collector ionization-coupled plasma mass-spectrometry in serum, urine, and feces. The relationship between bone Ca gain and loss was calculated using a compartment model. δ 44/42 Ca serum and δ 44/42 Ca urine were higher in children (n = 66, median age 13 years) compared with adults (n = 51, median age 28 years; p < 0.0001 and p = 0.008, respectively). δ 44/42 Ca serum increased with height in boys (p < 0.001, R 2 = 0.65) and was greatest at Tanner stage 4. δ 44/42 Ca serum correlated positively with biomarkers of bone formation (25-hydroxyvitaminD [p < 0.0001, R 2 = 0.37] and alkaline phosphatase [p = 0.009, R 2 = 0.18]) and negatively with bone resorption marker parathyroid hormone (PTH; p = 0.03, R 2 = 0.13). δ 44/42 Ca serum strongly positively correlated with tibial cortical BMD Z-score (n = 62; p < 0.001, R 2 = 0.39) but not DXA. Independent predictors of tibial cortical BMD Z-score were δ 44/42 Ca serum (p = 0.004, β = 0.37), 25-hydroxyvitaminD (p = 0.04, β = 0.19) and PTH (p = 0.03, β = −0.13), together predicting 76% of variability. In conclusion, naturally occurring Ca isotope ratios in different body compartments may provide a novel, non-invasive method of assessing bone mineralization. Defining an accurate biomarker of BMB could form the basis of future studies investigating Ca dynamics in disease states and the impact of treatments that affect bone homeostasis.

Mineral and bone disorder in chronic kidney disease (CKD-MBD) is a triad of biochemical imbalances of calcium, phosphate, parathyroid hormone and vitamin D, bone abnormalities and soft tissue calcification. Maintaining optimal bone health in children with CKD is important to prevent long-term complications, such as fractures, to optimise growth and possibly also to prevent extra-osseous calcification, especially vascular calcification. In this review, we discuss normal bone mineralisation, the pathophysiology of dysregulated homeostasis leading to mineralisation defects in CKD and its clinical consequences. Bone mineralisation is best assessed on bone histology and histomorphometry, but given the rarity with which this is performed, we present an overview of the tools available to clinicians to assess bone mineral density, including serum biomarkers and imaging such as dual-energy X-ray absorptiometry and peripheral quantitative computed tomography. We discuss key studies that have used these techniques, their advantages and disadvantages in childhood CKD and their relationship to biomarkers and bone histomorphometry. Finally, we present recommendations from relevant guidelines-Kidney Disease Improving Global Outcomes and the International Society of Clinical Densitometry-on the use of imaging, biomarkers and bone biopsy in assessing bone mineral density. Given low-level evidence from most paediatric studies, bone imaging and histology remain largely research tools, and current clinical management is guided by serum calcium, phosphate, PTH, vitamin D and alkaline phosphatase levels only.

Background Biomarkers and dual-energy X-ray absorptiometry (DXA) are thought to be poor predictors of bone mineral density (BMD). The Kidney Disease: Improving Global Outcomes guidelines suggest using DXA if the results will affect patient management, but this has not been studied in children or young adults in whom bone mineral accretion continues to 30 years of age. We studied the clinical utility of DXA and serum biomarkers against tibial cortical BMD (CortBMD) measured by peripheral quantitative computed tomography, expressed as Z-score CortBMD, which predicts fracture risk. Methods This was a cross-sectional multicentre study in 26 patients with CKD4 and 5 and 77 on dialysis. Results Significant bone pain that hindered activities of daily living was present in 58%, and 10% had at least one low-trauma fracture. CortBMD and cortical mineral content Z-scores were lower in dialysis compared with CKD patients (P = 0.004 and P = 0.02). DXA BMD hip and lumbar spine Z-scores did not correlate with CortBMD or biomarkers. CortBMD was negatively associated with parathyroid hormone (PTH; r = −0.44, P &lt; 0.0001) and alkaline phosphatase (ALP; r = −0.22, P = 0.03) and positively with calcium (Ca; r = 0.33, P = 0.001). At PTH &lt;3 times upper limit of normal, none of the patients had a CortBMD below −2 SD (odds ratio 95% confidence interval 7.331 to infinity). On multivariable linear regression PTH (β = −0.43 , P &lt; 0.0001), ALP (β = −0.36, P &lt; 0.0001) and Ca (β = 0.21, P = 0.005) together predicted 57% of variability in CortBMD. DXA measures did not improve this model. Conclusions Taken together, routinely used biomarkers, PTH, ALP and Ca, but not DXA, are moderate predictors of cortical BMD. DXA is not clinically useful and should not be routinely performed in children and young adults with CKD 4–5D.

No abstract