Final answer:
Unconjugated bilirubin is a non-water-soluble bile pigment circulating bound to albumin, usually processed in the liver into a water-soluble form. If not properly conjugated due to enzyme deficiencies, such as in neonatal jaundice, it can accumulate in the blood and potentially cause kernicterus. Diagnostic tests differentiate between unconjugated and conjugated forms of bilirubin.
Step-by-step explanation:
Free or unconjugated bilirubin is a bile pigment that is produced as a waste product when the spleen removes old or damaged red blood cells from circulation. As these breakdown products are transported to the liver, bilirubin is released into the blood. In its unconjugated form, bilirubin is not water-soluble, and thus cannot be excreted in urine directly. It travels in the bloodstream bound to albumin to the liver, where it is normally converted into its water-soluble form through conjugation with glucuronic acid in a process facilitated by the enzyme UDP glucuronyl transferase, producing conjugated bilirubin or bilirubin diglucuronide.
Conditions such as neonatal jaundice (unconjugated hyperbilirubinemia) occur when there is a buildup of unconjugated bilirubin in the blood due to insufficient activity of UDP glucuronyl transferase. High levels of unconjugated bilirubin can lead to health complications, including kernicterus, a form of brain damage.
Diagnostic tests can differentiate between conjugated and unconjugated bilirubin. The direct Van Den Bergh test detects conjugated bilirubin directly, while the indirect Van Den Bergh test is used to measure unconjugated bilirubin by adding alcohol to cause a color change with the Diazo reagent.