Three methods for the estimation of bilirubin in amniotic fluid are compared. The within-batch precision and recovery of bilirubin by each method has been studied, and the effects of the presence of haemoglobin, methaemoglobin, and methaemalbumin in varying concentrations have been investigated. Measurements on amniotic fluid from patients with rhesus isoimmunization have also been compared and regression equations calculated. The results of the three methods agree reasonably well so long as no haemoglobin degradation products are present. It is suggested that in the presence of these products a method involving organic solvent extraction of bilirubin gives the most accurate result.
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