Enzyme immunoassay for conjugated cholic and 1 beta-hydroxycholic acids in urine of early infancy.

A direct competitive heterologous enzyme immunoassay (EIA) for conjugated cholic acid (CA) was developed using horseradish peroxidase labeled antigen having a shorter bridge length than that of the immunogen. An appropriate dose-response curve for conjugated CA was obtained in the range of 0.05-50 ng/well. Specificity of the EIA proved satisfactory in terms of cross-reactivities to 23 kinds of related bile acids. The proposed method was evaluated to be useful for the determination of conjugated CA in urine with acceptable accuracy and inter- and intra-assay precision. The results of analysis showed a reverse relationship between age and urinary excretion ratio of conjugated 1 beta-hydroxy-CA to conjugated CA in the first 9 months after birth.