Jaundice, also known as icterus, is a yellowing of the skin, conjunctiva (clear covering over the sclera, or whites 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.
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 (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 increased 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 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 jaundice, is common, occurring 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 (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. Also, a group of parasites known as "liver flukes" live in the common bile duct, causing obstructive jaundice. 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 color from bile pigments. Patients often complain of severe itching.
Neonatal jaundice is usually harmless: this condition is often seen in infants around the second day after birth, lasting until day 8 in normal births, or to around day 14 in premature births. Serum bilirubin normally drops to a low level without any intervention required: the jaundice is presumably a consequence of metabolic and physiological adjustments after birth. In extreme cases, a brain-damaging condition known as kernicterus can occur; there are concerns that this condition has been rising in recent years due to inadequate detection and treatment of neonatal hyperbilirubinemia.