The text discusses the relationship between bilirubin and liver function. Elevated levels of unconjugated bilirubin can indicate prehepatic or hepatic jaundice, while an increase in conjugated bilirubin may suggest increased hemolysis or liver disease. Urobilinogen, a byproduct of bilirubin metabolism, can also indicate liver disease or damage when found in urine. Serum bilirubin levels are commonly used as a diagnostic marker for hepatic illnesses, as it reflects the liver's ability to process and secrete bilirubin. Neonatal jaundice, caused by high levels of unconjugated bilirubin in the blood, is a result of the breakdown of red blood cells. A high concentration of conjugated bilirubin in the plasma can indicate impaired liver function or hepatocellular disease.