Comparison of various methods for amniotic fluid ΔOD450 bilirubin measurement

BackgroundThe purpose of this study was to investigate the degree of ΔOD450 method variability and its effect on ΔOD450 measurements between selected clinical laboratories in the U.S.MethodFour amniotic fluid specimens were sent to 7 clinical laboratories in the U.S. for ΔOD450 analysis. In addition, scanning spectrophotometric data from 152 amniotic fluid samples were used to compare ΔOD450 values calculated using both log and linear OD scales.ResultsWe 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 ΔOD450 measurements were remarkably similar. The exception was 1 sample that was subjected to chloroform extraction. The ΔOD450 measurement on this sample was 82% lower than the mean. On average, ΔOD450 results determined from a linear OD scale were 37% lower than those determined from a log scale.ConclusionAlthough there is no standard method for performing the ΔOD450, inter-laboratory variation of ΔOD450 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 ΔOD450 results.