Assessing Bone Calcium Content in Children With Kidney Disease Treated With Two Different Medicines

Lay Summary of Background and Rationale: The growing bones of children need calcium in order to mineralise (become strong). Children with kidney failure (called chronic kidney disease; CKD) or on dialysis can often be calcium deficient. They are given medications with extra calcium to help their bones mineralise. However, there is currently no practical way of measuring bone mineralisation. Doctors may perform special x-rays, but it takes many months before any bone structure problems become apparent on X-rays. Doctors giving children additional calcium do not know how much to give. Sometimes children are given too little and their bones do not mineralise adequately, or they are given too much, and the excess calcium is deposited in their arteries causing vascular calcification. Timely and practical ways of measuring bone mineralisation are needed so doctors can accurately determine the amount of calcium containing medicines they give. The CAL-BAL trial will evaluate a novel potential biomarker of bone mineralisation: the calcium isotope ratio (δ44/42Ca) which will be measured in blood and urine. The trial will collect information on δ44/42Ca for patients with CKD or on dialysis for 28 weeks. It will measure how δ44/42Ca changes when a patient switches from a medicine containing calcium to one not containing calcium. It will also evaluate the association between δ44/42Ca and established biomarkers of bone formation and repair. The data collected in CALBAL will not by itself allow doctors to decide whether δ44/42Ca is good biomarker of bone mineralisation. However, it will provide additional biological and clinical information that will further clarify its usefulness as biomarker for further research. Together with information from previous studies done by the Chief Investigator which measured the typical δ44/42Ca of healthy children and children with CKD and on dialysis, the data collected in CAL-BAL may inform the design of a future randomised trial of standard-of-care compared to an approach where δ44/42Ca results are used to prescribe the amount of medicine containing calcium children with CKD or on dialysis are given.