Bilirubiinifractions

Bilirubin is a yellow pigment formed from the breakdown of heme, a component of hemoglobin found in red blood cells. When red blood cells are broken down, primarily in the spleen and liver, hemoglobin is released. This hemoglobin is then processed into biliverdin, which is subsequently reduced to bilirubin. The body's ability to process and eliminate bilirubin is crucial for health, and disruptions in this process can lead to jaundice, a yellowing of the skin and eyes.

Bilirubin exists in the bloodstream in different forms, referred to as fractions. The primary fractions are unconjugated bilirubin and conjugated bilirubin. Unconjugated bilirubin, also known as indirect bilirubin, is lipid-soluble and bound to albumin in the blood for transport to the liver. In the liver, unconjugated bilirubin is taken up by liver cells and undergoes a process called conjugation, where it is chemically attached to glucuronic acid. This process makes bilirubin water-soluble and is called conjugated bilirubin, also known as direct bilirubin.

Once conjugated, bilirubin is excreted from the liver into the bile, which is then transported to the small intestine. In the intestine, bacteria further metabolize conjugated bilirubin into urobilinogen and stercobilin. Urobilinogen is partially reabsorbed into the bloodstream and excreted by the kidneys, giving urine its characteristic yellow color. The remaining stercobilin is excreted in the feces, giving stool its brown color. Measuring the levels of bilirubin fractions in the blood is an important diagnostic tool for evaluating liver function and identifying the cause of jaundice. Elevated levels of unconjugated bilirubin may indicate increased red blood cell breakdown or impaired liver uptake, while elevated conjugated bilirubin can suggest problems with bilirubin excretion from the liver or bile ducts.