Once the urobilinogen is exposed to the environment upon urination, it is oxidized to urobilin, which makes the urine appear dark in instances of common bile duct obstruction.
It is a sensitive marker for biliary obstruction, and early acute hepatitis as well.
Since TheGeeze has explained you facts about Urobilin there is no need to repeat his words and I hope that you are satisfied with his answer. He didn’t mention that urolbilin is brown bile pigment formed from urobilinogens. It can be found in feces and in small amounts of urine. Also you need to know that urobilin is one of the final products of hemoglobin breakdown.
I hope that this is satisfying answer to your question.
So you were doing urine analysis. Was there any particular reason for this or just regular checkup?
I hope that everything is fine and that you will not get any of those infections which can be really nasty sometimes. Good luck.