ESPE Abstracts

Background: In paediatric patients with metabolic bone diseases, measurement of the concentrations of minerals including inorganic phosphate is often indicated, and hypophosphataemia is a clinically manageable biochemical disorder. The clinical interpretation of plasma or serum phosphate concentrations depends, to a certain extent, on the age- and gender-specific reference intervals applicable to the laboratory methods employed.

Whereas harmonised phosphate reference intervals based on consensus have been published by professional groups, recent large-scale prospective studies have established paediatric reference intervals for many analytes by recruiting healthy young subjects from their populations and using the direct method for establishing reference intervals.

Methodology: A literature search was conducted to identify (1) prospective, a priori studies for the establishment of paediatric reference intervals, and (2) published consensus paediatric phosphate reference intervals. The age- and gender-specific phosphate reference intervals from these sources were compared and contrasted with one another.

Results: We have identified two sources of harmonised paediatric phosphate reference intervals based on consensus among healthcare professionals, i.e. the Australasian Association of Clinical Biochemists (AACB) and the Pathology Harmony Group (United Kingdom), and four separate well-designed, large-scale prospective studies for the direct establishment of paediatric reference intervals for plasma/serum phosphate concentrations.

The consensus reference intervals for paediatric phosphate concentrations from the AACB and the Pathology Harmony Group are partitioned according to age but not gender. Although prospective studies on healthy paediatric populations have shown that in general, phosphate concentrations in plasma and serum gradually decrease from birth until adulthood, the Pathology Harmony Group currently recommends a single age partition for plasma and serum phosphate concentrations in both genders from 1 to 16 years of age. Among the prospective studies, age-specific upper and lower reference limits in boys are generally either the same as or slightly higher than the corresponding reference limits in girls. From birth up to 13 years of age, all consensus lower reference limits (LRLs) for phosphate in both genders recommended by the AACB and the Pathology Harmony Group are numerically lower than the corresponding age- and gender-specific phosphate LRLs established using direct methods in the above four prospective studies.

Conclusion: Age-partitioned phosphate reference limits are important for clinical practice in detecting paediatric hypophosphataemia. The harmonised paediatric phosphate LRLs based on consensus and published by the AACB and the Pathology Harmony Group may lack diagnostic sensitivity in detecting mild to moderate hypophosphataemia especially in young children.