The status of bilirubin measurements in U.S. laboratories: why is accuracy elusive?

In 2003, the Chemistry Resource Committee of the College of American Pathologists introduced a new specimen in the Neonatal Bilirubin Survey. The specimen, consisting of human serum enriched with unconjugated bilirubin and thus resembling a clinical specimen, brought about an improvement in the accuracy of the measurement of bilirubin by laboratories participating in the Neonatal Bilirubin Survey. There was also an improvement in the specificity of methods measuring direct bilirubin. However, persisting inaccuracies and variability in laboratory performance have been traced to calibrators consisting of bovine serum spiked with unconjugated bilirubin and ditaurobilirubin; bovine serum causes underestimation of both bilirubins by 8 major chemical analyzers. To eradicate inaccuracy calibrators and Survey specimens should be made in human instead of bovine serum.