Jaundice, also known as icterus (attributive adjective: "icteric"), is a yellowing of the skin, sclera (the white of the eyes) and mucous membranes caused by increased levels of bilirubin in the human body (or the body of another red blooded animal). Usually the concentration of bilirubin in the blood must exceed 2?3 mg/dL for the coloration to be easily visible. Jaundice comes from the French word jaune, meaning yellow.
Causes of jaundice
When red blood cells die, the heme in their hemoglobin is converted to bilirubin in the spleen and in the hepatocytes in the liver. The bilirubin is processed by the liver, enters bile and is eventually excreted through feces.
Consequently, there are three different classes of causes for jaundice. Pre-hepatic or hemolytic causes, where too many red blood cells are broken down, hepatic causes where the processing of bilirubin in the liver does not function correctly, and post-hepatic or extrahepatic causes, where the removal of bile is disturbed.
Pre-hepatic
Pre-hepatic (or hemolytic) jaundice is caused by anything which causes an increased rate of hemolysis (breakdown of red blood cells). In tropical countries, malaria can cause jaundice in this manner. Certain genetic diseases, such as sickle cell anemia and glucose 6-phosphate dehydrogenase deficiency can lead to increase red cell lysis and therefore hemolytic jaundice. Defects in bilirubin metabolism also present as jaundice. Jaundice usually comes with high fevers.
The laboratory findings include:
- Urine: no bilirubin present, urobilirubin > 2 units (except in infants where gut flora has not developed).
- Serum: increased unconjugated bilirubin.
Hepatic
Hepatic causes include acute hepatitis, hepatotoxicity and alcoholic liver disease, whereby cell necrosis reduces the liver's ability to metabolise and excrete bilirubin leading to a build up in the blood. Less common causes include primary biliary cirrhosis, Gilbert's syndrome (a genetic disorder of bilirubin metabolism which can result in mild jaundice, which is found in about 5% of the population) and metastatic carcinoma. Jaundice seen in the newborn, known as neonatal jaudice, is common, occuring in almost every newborn as hepatic machinery for the conjugation and excretion of bilirubin does not fully mature until approximately two weeks of age.
Laboratory Findings: Urine: bilirubin present, Urobilirubin > 2 units but variable (Except in children)
Post-hepatic
Post-hepatic (or obstructive) jaundice, also called cholestasis, is caused by an interruption to the drainage of bile in the biliary system. The most common causes are gallstones in the common bile duct, and pancreatic cancer in the head of the pancreas. Other causes include strictures of the common bile duct, ductal carcinoma, pancreatitis and pancreatic pseudocysts. A rare cause of obstructive jaundice is Mirizzi's syndrome.
The presence of pale stools and dark urine suggests an obstructive or post-hepatic cause as normal feces get their colour from bile pigments. Patients sometimes also complain of itching.
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