Final answer:
Indirect bilirubin or unconjugated bilirubin is another name for pre-liver bilirubin. It becomes direct bilirubin or bilirubin mono and di-glucuronide once it is processed by the liver, rendering it water-soluble and excretable.
Step-by-step explanation:
Another name for 'pre-liver bilirubin' is indirect bilirubin or unconjugated bilirubin. This form of bilirubin is not water-soluble and circulates in the bloodstream bound to albumin.
After it reaches the liver, bilirubin is conjugated with glucuronic acid by the enzyme UDP glucuronyl transferase, transforming it into direct bilirubin or bilirubin mono and di-glucuronide, which is water-soluble and can be excreted into the bile duct and eventually into the intestine.
In the intestine, it is further converted into stercobilinogen and then into stercobilin, which contributes to the characteristic brown color of feces. Direct Van Den Bergh test specifically identifies the presence of conjugated bilirubin, which reacts with Diazo reagent to give a purple red color without the need of adding alcohol - this differentiates it from indirect bilirubin.