This report presents a comparative study of gallstone and gallbladder bile composition from 100 unselected American patients, 23 with pigment and 77 with cholesterol cholelithiasis. Cholesterol stones were predominantly composed of cholesterol, whereas pigment stones were mainly composed of an unidentified residue, bilirubin, and bile salts. The residue in pigment stones was not calcium bilirubinate, which sharply contrasts with the composition of bile pigment calcium stones found in Japanese subjects. Bile composition of the two groups differed in that the cholesterol content of biles surrounding pigment stones was significantly less than that of biles surrounding cholesterol stones. Bilirubin in biles was conjugated, but the pigment extracted from stones was unconjugated bilirubin. This study indicates that (1) pigment stones account for an appreciable percentage of gallstone specimens found at cholecystectomy, and (2) pigment stone formation involves the precipitation of bilirubin, bile salts, and unidentified material which is not calcium bilirubinate.
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