Bilirubin

When bilirubin levels are high, a condition called jaundice (a yellowing of the skin and the whites of the eyes) occurs and further testing is needed to determine the cause. Too much bilirubin may mean that too many red cells are being destroyed, or that the liver is incapable of removing bilirubin from the blood.

It is not uncommon to see high bilirubin levels (sometimes called neonatal bilirubin) in newborn babies (typically 1–3 days old). Within the first 24 hours of life, up to 50% of full-term newborns, and an even greater percentage of pre-term babies, may have a high bilirubin level. Before birth, bilirubin produced in the fetus is transferred by the placenta to the mother’s circulation. After birth, the infant’s liver has to process this bilirubin, but it takes several days to adapt, causing the bilirubin concentration to rise in the blood.

At birth, the newborn lacks the intestinal bacteria that help process bilirubin. This is not abnormal and resolves itself within a few days. In other instances, newborns’ red blood cells may have been destroyed because of blood type incompatibilities between the mother and the baby.

In adults or older children, bilirubin is measured to diagnose and/or monitor liver diseases (such as cirrhosis, hepatitis, or gallstones). Patients with sickle cell disease or other causes of haemolytic anaemia may have episodes where excessive red blood cell destruction takes place, increasing bilirubin levels.

A doctor usually orders a bilirubin test in conjunction with other laboratory tests (alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase) for a patient who shows signs of abnormal liver function. A bilirubin level may be ordered when a patient:

• shows evidence of jaundice
• has a history of drinking excessive amounts of alcohol
• has suspected drug toxicity
• has been exposed to hepatitis viruses

Other symptoms that may be present include:

• dark, amber-coloured urine
• nausea/vomiting
• abdominal pain and/or swelling
• fatigue and general malaise that often accompany chronic liver disease

Determining a bilirubin level in newborns with jaundice is considered standard medical care.

Newborns
Excessive bilirubin damages developing brain cells in infants and may cause mental retardation, physical abnormalities or blindness. It is important that bilirubin in newborns does not get too high. When the level of bilirubin is above a critical threshold, special treatment is used to reduce it. An excessive bilirubin level may result from the breakdown of red blood cells (RBCs) due to Rhesus blood typing incompatibility. (If the mother is Rhesus negative [Rh-], the father is Rhesus positive [Rh+] and the fetus is Rh+, then the mother develops antibodies against the newborn baby's RBCs, which are destroyed.)

Adults and children
Doctors may request bilirubin tests (along with other tests, especially when jaundice is present) to determine if liver damage exists. Bilirubin levels can be used to monitor the progression of jaundice and to determine if it is the result of red blood cell breakdown or liver disease. This can be done by measuring two different chemical forms of bilirubin — direct (or conjugated) and indirect (or unconjugated) bilirubin. If the direct bilirubin is elevated there may be some kind of blockage of the liver or bile duct, perhaps due to gallstones, hepatitis, trauma, a drug reaction, or long-term alcohol abuse. If the indirect bilirubin is increased, haemolysis (undesirable breakdown of red blood cells) may be the cause.

Although bilirubin may be toxic to brain development in newborns (up to the age of about 2–4 weeks), high bilirubin in older children and adults does not pose the same threat. In older children and adults, the 'blood-brain barrier' is more developed and prevents bilirubin from crossing this barrier to the brain cells. Elevated bilirubin levels in children or adults, however, strongly suggest a medical condition that must be investigated and treated.

Jaundice results from high levels of bilirubin. Increases in bilirubin may be due to metabolic problems, obstruction of the bile duct, physical or chemical damage to the liver (cirrhosis), or an inherited abnormality (Gilbert’s, Rotor’s, Dubin-Johnson or Crigler-Najjar syndromes).