Comparison of various methods for amniotic fluid ΔOD450 bilirubin measurement

Background: The purpose of this study was to investigate the degree of Delta OD450 method variability and its effect on Delta OD450 measurements between selected clinical laboratories in the U.S. Method: Four amniotic fluid specimens were sent to 7 clinical laboratories in the U.S. for Delta OD450 analysis. In addition, scanning spectrophotometric data from 152 amniotic fluid samples were used to compare Delta OD450 values calculated using both log and linear OD scales. Results: We found that no 2 laboratories used exactly the same method and no laboratory used precisely the same method as originally described by Liley. Despite the varied methods, the Delta OD450 measurements were remarkably similar. The exception was 1 sample that was subjected to chloroform extraction. The Delta OD450 measurement on this sample was 82% lower than the mean. On average, Delta OD450 results determined from a linear OD scale were 37% lower than those determined from a log scale. Conclusion: Although there is no standard method for performing the Delta OD450, inter-laboratory variation of Delta OD450 results is remarkably small. As our and other previous studies have reported, these data suggest that both chloroform extraction and use of a linear scale have the potential to result in lower Delta OD450 results. (c) 2007 Elsevier B.V. All rights reserved.