Jaundice is the medical term for yellow discoloration of the skin, sclera (whites of the eye) and deeper tissues like the mucus membrane of the mouth usually as a result of high levels of bilirubin in the blood. The word ‘jaundice’ essentially means yellow color (Latin ~ glabinus, French ~ jaunisse). It is commonly referred to as yellow jaundice but this makes the term redundant (yellow yellow).
The term icterus is often used concurrently with jaundice, however, icterus indicates a yellow discoloration of the sclera of the eye.
What Causes Jaundice?
Formation of Bilirubin
The body is constantly breaking down old red blood cells (RBC’s/erythrocytes) when these cells reach the end of its lifespan in the circulation (approximately 120 days) or become damaged. The RBC’s are renewed by the maturation of hematopoietic stem cells found in tissue like the bone marrow.
The RBC’s rupture and hemoglobin is consumed by macrophages (phagocytosis). The hemoglobin is then split into heme and globin. Heme is further broken down into iron and another molecule known as tetrapyrrole which is formed into biliverdin. From this biliverdin, free bilirubin (unconjugated bilirubin) is made and it circulates in the blood stream.
The free bilirubin is quickly taken up by the liver, conjugated and released by the liver cells as conjugated bilirubin which is emptied with bile into the intestine. The enzyme glucoronyl transferase is responsible for the conjugation of bilirubin with glucoronic acid. The liver can easily excrete the conjugated bilirubin, thereby removing this waste product from the body, however, free bilirubin cannot be excreted by the liver.
Most of the conjugated bilirubin will be passed out in the feces and some are converted into urobilinogen by the action of bacteria in the gut. Small amounts of urobilinogen are absorbed back into the blood stream and then passed out again by the liver as bile or excreted by the kidneys in urine.
Free bilirubin is constantly circulating in the blood stream and averages about 0.5mg/dL in a normal state. Any disruption increases the free and conjugated bilirubin in the blood. The yellowish discoloration of the skin that is typical of jaundice becomes evident when the bilirubin level reaches 1.5mg/dL.
An excess of bilirubin may be a result of:
- Excess breakdown of red blood cells – hemolytic jaudice.
- Inability of the liver to conjugate bilirubin – non-hemolytic hyperbilirubinemia. This is also seen in neonatal jaundice (physiological jaundice) which occurs in newborn babies, usually within the first 2 weeks of life.
- Failure of the liver cells to excrete bilirubin into bile – hepatocellular jaundice.
- Obstruction of the flow of bile out of the liver – obstructive jaundice.
The pathophysiology and causes are further explained in the article on Types of Jaundice.
Other Causes of a Yellowish Skin
- Hypercarotenemia occurs in people who eat large amounts of foods that are high in carotene, like tomatoes and carrots. This causes a yellowish discoloration of the skin, but not the sclera of the eye, and is more pronounced on the face, palms of the hand and soles of the feet. This yellow tinge of the skin is not associated with jaundice due to hyperbilirubinemia and may also be seen in hypothyroidism.
- Patients with pernicious anemia may appear a pale yellow, sometimes described as lemon-yellow, due to a combination of pallor and jaundice.
- Wilson’s disease results in jaundice as a result of copper deposition in the tissues. This is due to the body’s inability to metabolize copper which is a major component of skin pigmentation. Other causes of copper toxicity (poisoning) may also result in jaundice.