BackgroundSevere hypercalcaemia is a rare but clinically significant condition in infancy and childhood. Parathyroid hormone-related peptide (PTHrP)-mediated hypercalcaemia resulting from a malignancy is rare and only a handful of case reports have outlined its incidence alongside a benign condition.ObjectivesTo describe the diagnostic workup and management of an infant with hypercalcaemia, renal dysplasia, and elevated PTHrP levels.DesignCase report.SettingThe Victoria Hospital campus of the London Health Sciences Centre in London, Ontario, Canada.PatientsA child with congenital anomalies of the kidneys and urinary tract (CAKUT), stage 2 chronic kidney disease (CKD), and renal dysplasia who presented with severe hypercalcaemia.MeasurementsWeight, renal ultrasound, creatinine, cystatin C, eGFR, calcium, urea, bicarbonate, serum sodium, fractional sodium excretion, urine calcium to creatinine ratio, PTH, TSH, Free T4, AM cortisol, HMA, VMA, 25-vitamin D, 1,25 dihydroxy-vitamin D, calcitriol, vitamin A, ACE levels, skull and chest x-rays, alkaline phosphatase, CBC, tumour lysis profile, catecholamine breakdown, whole-body MRI, PTHrP.MethodsFull diagnostic workup and patient management. Patient treated with intravenous hydration, furosemide, calcitonin and CalciLo.ResultsPTHrP was elevated and no evidence of a malignancy was found. Treatment consisting of a low-calcium CalciLo diet (in place of breast milk) adequately controlled the patient’s hypercalcaemia. Hypercalcaemia associated with CAKUT in infancy is not all that uncommon and was reported in 15/99 infants in another study, most of whom had a suppressed PTH similar to that of our patient. PTHrP was not measured in these cases and may have also been elevated.LimitationsThe study is limited in that it is a description of a single patient case. Future measurement of PTHrP in similar patients is necessary to confirm our results.ConclusionsThe possibility of elevated PTHrP levels must be considered in patients with known renal dysplasia who are differentially diagnosed with hypercalcaemia.