Reflections on the standardization of total bilirubin in neonatal serum

A study is described on the standardization of the determination of neonatal total bilirubin. A wide variation in results was shown in surveys held in The Netherlands and Germany and the reasons for this variation were sought. The suitability of commercial bilirubin standards and direct reading instruments, widely used in the neonatal field, was tested by comparing all measurements with those obtained with the candidate reference method. We found differences between the stated values and those obtained by the reference method. However, a bias was also shown to exist between the results measured with the direct reading instruments and those obtained with the reference method, explaining at least qualitatively, the variation seen in the surveys. In addition, problems in the calibration of the DuPont ACA are discussed.