Under normal circumstances, bile is discharged into the intestine through the bile ducts, and the bilirubin in the bile is broken down by bacteria into fecal bilirubin and urobilirubin, part of which is excreted with the stool, which is yellow in color; the other part is reabsorbed into the liver to re-synthesize bilirubin and then secreted into the intestine, and the absorbed part of urobilirubin is not metabolized by the liver and goes directly into the blood and is excreted through the kidneys. Therefore, the urine is normally positive for urobilinogen and negative for bilirubin. If the common bile duct is obstructed, bilirubin cannot be excreted into the intestinal lumen, no urobilinogen or fecal bilirubin is formed, the stool is clay-colored, bilirubin enters the blood, the whole body is yellowish, excreted by the kidneys, urinary bilirubin is positive and urobilinogen is negative.