Studies of the extraction of bilirubin from human amniotic fluid.

The recovery of unconjugated bilirubin from human amniotic fluid was studied using dichloromethane, chloroform/isopropanol (3:1 vol/vol), and chloroform/ methanol (3:1 vol/vol) extraction of human amniotic fluid that had been supplemented with bilirubin at various concentrations. Results were compared with those obtained with conventional chloroform extraction. Mean recoveries were found to be only 28% for chloroform and 25% for dichloromethane. When the polarity of chloroform was increased by the addition of an alcohol, the mean recovery increased to only 40% for chloroform/isopropanol and 38% for chloroform/ methanol. These results suggest that extraction methods for determination of amniotic fluid "delta OD(450)" (visible spectrophotometric absorbance [optical density] of bilirubin at 450 nm) tend to underestimate the result when compared with the nonextraction (direct-scan) method, on which the Liley Prognostication Chart is based. This finding should be clinically significant, particularly if extraction and direct-scan methods are used to monitor the condition of the same patient.