• paediatric chemistry
• bone
• phosphate
• reference limit

Clinical indications for the measurement of serum or plasma concentrations of inorganic phosphate (hereafter referred to as phosphate) in paediatric patients include metabolic bone disorders, parathyroid abnormalities, malnutrition, renal failure and so on. To a certain extent, the interpretation of serum or plasma phosphate concentrations depends on the age-specific and gender-specific reference intervals used in conjunction with other clinical and laboratory findings. In our clinical practice, we have encountered some marked differences between serum phosphate reference intervals directly established using a priori methods and consensus serum phosphate reference intervals from professional groups including the Australasian Association of Clinical Biochemists (AACB)1 and the Pathology Harmony Group (UK).2 In this correspondence, we highlight the clinical implications of the differences in reference limits for serum phosphate concentrations in the diagnosis of hypophosphataemia in paediatric patients.

Most clinical laboratories do not have enough resources to recruit sufficient numbers of healthy children to establish their own reference intervals. In the past, methods that employ laboratory data mining, also known as indirect methods, were widely used to generate paediatric reference intervals. Those indirect methods usually use statistical techniques, such as the methods proposed by Hoffmann3 or Bhattacharya4, to separate overlapping distributions of healthy and diseased populations within existing laboratory data. More recently, large-scale prospective studies have established paediatric reference intervals for many analytes by recruiting healthy young subjects from their populations (direct method). The Canadian Laboratory Initiative on Pediatric Reference Intervals Project has addressed major gaps in this field and provides a clinically useful database of directly …