Conjugated hyperbilirubinemia serves as the clinical surrogate marker for the recognition of cholestasis, because of the difficulty in obtaining specific information regarding bile acid metabolism. We therefore have developed a practical method of bile acid analysis that permits identification of all bile acids including ester sulfates, glucuronides, and labile allylic bile acids that occur with inborn errors of bile acid metabolism. Bile acids are extracted from serum [50 μl] or urine [0.8 to 2.0 ml, standardized to creatinine content] and reacted with 1-bromo-4,5-dimethoxycoumarin to form fluorescent carboxylic acid esters that are detected by HPLC analysis after preliminary purification by TLC. When needed, the use of cholylglycine hydrolase enzyme hydrolysis and internal standardization permit quantification of each bile acid species.

In applying this technology in the neonatal intensive care unit both to monitor the course of intravenous hyperalimentation and to diagnose inborn and acquired errors in bile acid metabolism, we have found that concurrent administration of medications can cause conjugated hyperbilirubinemia mimicking cholestasis. Thus the normal urinary bile acid pattern in which cholic acid predominates shifts to a predominance of chenodeoxycholic acid-3-sulfate during development of conjugated hyperbilirubinemia, with return to normal after the medication is discontinued. This benign disorder, attributable to competition for organic anion transport, should be differentiated from the occurrence of cholestasis that may progress to cirrhosis.

Although surrogate markers will continue to be useful, introduction of routine urinary bile acid analysis will identify specific abnormalities in bile acid metabolism and excretion.