Icterus, commonly known as jaundice, is the yellowish discoloration of the skin, mucous membranes, and the whites of the eyes. This yellowing results from an excessive buildup of bilirubin in the bloodstream, a condition called hyperbilirubinemia. Icterus is not a disease but a symptom indicating an underlying imbalance in the body’s process of producing, processing, or eliminating bilirubin.
How Bilirubin Leads to Yellowing
Bilirubin is a yellowish-orange pigment that is a natural byproduct of red blood cell breakdown. When old red blood cells are metabolized, the iron-containing heme component is converted into unconjugated (indirect) bilirubin. This initial form of the pigment is highly insoluble in water.
Because it is water-insoluble, unconjugated bilirubin must bind to the blood protein albumin to travel to the liver. Inside the liver cells, the enzyme UDP-glucuronosyltransferase converts it into conjugated (direct) bilirubin by adding glucuronic acid. This modification makes the bilirubin water-soluble, which is necessary for excretion.
The liver secretes conjugated bilirubin into the bile, which travels through the bile ducts into the small intestine. There, bacteria convert it into stercobilin, which colors the stool, and urobilinogen, which is partially excreted in the urine. Icterus occurs when bilirubin production exceeds the liver’s processing capacity, or when the liver or ducts are blocked. The pigment then accumulates in the blood and deposits in tissues, causing the yellow appearance.
Categorizing the Underlying Causes
Medical professionals classify the causes of icterus based on where the problem occurs in the bilirubin processing pathway: pre-hepatic (before the liver), hepatic (within the liver), or post-hepatic (after the liver). This classification helps narrow the source of hyperbilirubinemia.
Pre-Hepatic Icterus
Pre-hepatic icterus occurs due to excessive red blood cell breakdown, overwhelming the liver’s capacity to process bilirubin. This condition, often seen in hemolytic anemias, results in a significant increase in unconjugated bilirubin in the blood.
Hepatic Icterus
Hepatic icterus arises from damage or dysfunction within the liver cells, impairing their ability to process bilirubin. Conditions like viral hepatitis, alcohol-related liver disease, and cirrhosis cause this damage, leading to elevated levels of both unconjugated and conjugated bilirubin.
Post-Hepatic Icterus
Post-hepatic icterus, also known as obstructive jaundice, happens after bilirubin has been processed by the liver but cannot be properly excreted. This results from a blockage in the bile ducts that prevents the flow of bile into the intestine. Common causes include gallstones lodged in the ducts, inflammation of the pancreas, or tumors pressing on the biliary system.
Physiological Jaundice in Newborns
Physiological jaundice is a common, temporary form of icterus seen in newborns, affecting over 50% of full-term babies. It results from an immature liver that is inefficient at conjugating bilirubin, combined with a higher turnover rate of red blood cells. This leads to a transient rise in unconjugated bilirubin that typically peaks around the second to fourth day of life and resolves as the liver matures.
Diagnosis and Medical Management
Diagnosis begins with a physical examination and medical history, followed by specific blood tests. A blood panel measures the total bilirubin level and fractionates it into its conjugated (direct) and unconjugated (indirect) components. Analyzing this ratio is crucial for determining if the problem is pre-hepatic, hepatic, or post-hepatic.
Further blood tests, such as liver function tests, assess the health of the liver cells and bile ducts. If blood work suggests an obstruction, imaging studies are ordered, typically starting with an abdominal ultrasound. Imaging allows physicians to visualize the liver, gallbladder, and bile ducts to check for masses, gallstones, or blockages causing the post-hepatic condition.
The management of icterus is determined by the underlying cause identified through diagnosis. In adults, treatment focuses on resolving the specific condition, such as administering antiviral drugs for hepatitis or performing surgery to remove gallstones or tumors. For newborns with moderate to severe physiological jaundice, phototherapy is a common and effective treatment. This involves placing the infant under special blue-green lights that change the shape of bilirubin molecules, allowing them to be more easily excreted in the urine and stool without requiring liver conjugation.