Commutability assessment of candidate reference materials for total bilirubin assays in neonates

Neonatal total bilirubin (TBIL) measurements are the cornerstone for treatment decisions in neonatal hyperbilirubinemia. However, neonatal TBIL assays suffer from substantial inter-assay differences and standardization is hampered by the lack of commutable secondary reference materials. Therefore, the aim of this study was to assess commutability of candidate reference materials (RMs) to support standardization efforts.

Three types of materials were investigated as candidate RMs: bilirubin-spiked serum materials prepared by the Dutch EQA provider SKML, residual material from neonatal exchange transfusions, and NIST SRM916b material dissolved in adult serum. Commutability of these materials was assessed using the prediction interval and difference in bias approaches. To this end, all candidate RMs and clinical samples were measured on ten different routine methods and compared to the reference measurement procedure.

For three methods, commutability could not be assessed due to too high non-selectivity. The exchange transfusion material demonstrated the highest degree of commutability, the highest TBIL concentration being commutable for all methods. Also, the two SRM-spiked samples with the highest TBIL concentrations showed to be commutable for six out of seven selective methods, except for the Ortho Vitros XT3400 platform.

Exchange transfusion materials provide a robust neonatal serum-based material which can be used as secondary reference material and as EQA material to support and monitor future efforts to improve standardization of neonatal TBIL assays.