Laboratory performance in neonatal bilirubin testing using commutable specimens: a progress report on a College of American Pathologists study.

CONTEXT: In 2003 the Chemistry Resource Committee of the College of American Pathologists introduced a commutable specimen in the Neonatal Bilirubin Surveys. This specimen was intended to help evaluate all bilirubin methods.
OBJECTIVE: To evaluate the effect of commutable specimens on the performance of selected clinical analyzers in measuring neonatal bilirubin from 2003 through 2006.
DESIGN: A human serum-based specimen enriched with unconjugated bilirubin in human serum has been included since 2003 in the Neonatal Bilirubin Surveys. The bilirubin values of these specimens were determined by the reference method and used to evaluate results reported by various chemistry analyzers.
RESULTS: Coefficients of variation for College of American Pathologists All Data ranged from 4.9% to 6.2% for the Neonatal Bilirubin Survey. However, coefficients of variation for the 4 major instrument groups (Dimension, Olympus, Synchron, and Vitros), which report 65% of all results, varied from 2% to 3%. College of American Pathologists All Data mean bilirubin values were within 0.46 mg/dL (7.8 micromol/L) of the reference method mean in 2003; in subsequent years these differences became larger, peaking at 1.87 mg/dL (32 micromol/L) in 2005.
CONCLUSIONS: The large systematic error of bilirubin measurements is due primarily to failure of instrument manufacturers to produce reliable bilirubin calibrators. Primary calibrators should consist of human serum enriched with unconjugated bilirubin. Bilirubin values must be assigned by the reference method, the performance and robustness of which are reported in this article. Secondary calibrators distributed to users must be traceable to primary calibrators.