Frequency and aetiology of hypercalcaemia. 
Hypercalcaemia is rare in children and may present with characteristic signs/symptoms or coincidentally following investigations for a variety of non-specific conditions.  The aetiologies of childhood hypercalcaemia are diverse.  Untreated sustained hypercalcaemia has serious clinical consequences.  However there is limited data regarding the true frequency and aetiologies of childhood hypercalcaemia.  To determine the frequency of severe childhood hypercalcaemia in routine clinical practice.  The laboratory database was searched for all children (0-17 years) with severe hypercalcaemia defined as non-adjusted ≥2.90 mmol/L from 2007-2012.  Hypercalcaemia was categorised as either transient (1 day) or sustained (≥2 consecutive days).  Retrospective analysis of all cases of sustained severe hypercalcaemia was performed to identify the underlying aetiology.  Over the 5 year period, 206 children were identified as severely hypercalcaemic ≥2.90 mmol/L (0.3% all 61,380 calcium requests).  Of these 131 (63.3%) children were classified as having sustained hypercalcaemia.  The frequency of severe hypercalcaemia was highest in neonates (42% of sustained cases) and was inversely related to age.  Sepsis was the most common aetiology (24%), particularly in neonates where it accounted for 41% of all causes of neonatal hypercalcaemia.  Endocrine aetiologies included congenital adrenal hyperplasia (2 cases), fat necrosis (1), Addison's disease (2).  A genetic cause was identified in 3 children (2 familial hypocalciuria hypercalcaemia, 1 Williams syndrome).  Sustained hypercalcaemia affects 1 in 500 children in a general hospital setting.  The frequency was highest in neonates and underlying aetiology differed markedly with age.  All children with sustained hypercalcaemia require thorough investigation to determine the underlying aetiology to ensure appropriate management.