When bilirubin concentrations in the blood increase it leads to a condition called jaundice (yellowing of the skin and/or the whites of the eyes). Further testing is often needed to help doctors find out the cause of the high bilirubin. Too much bilirubin may mean that too many red blood cells are being destroyed or liver damage is present.
It is not uncommon to see high unconjugated bilirubin concentrations in newborn babies from the second to the seventh day of life. This transient condition is called physiological jaundice. Bilirubin concentrations rarely peak higher than five times the upper limit of normal. Up to 50% of full-term newborns and an even greater percentage of pre-term babies may have jaundice. The newborn’s liver is not fully mature and is unable to process bilirubin fast enough. Physiological jaundice is not abnormal and resolves within a few days.
Newborn jaundice is likely to be abnormal if it persists longer than 8 - 14 days, when it could be caused by abnormal metabolism in the liver or malformation of the bile ducts. If the jaundice is present at birth and is caused by an elevated unconjugated bilirubin concentration, the newborns’ red blood cells may be being destroyed because of blood incompatibility between the baby and mother, called haemolytic disease of the newborn.
In adults or older children, bilirubin is measured to diagnose and 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 concentrations in the blood.
A doctor usually requests a bilirubin test in conjunction with other laboratory tests including ALP, AST and ALT as a group called liver function tests (LFTs) when a patient has a history, signs or symptoms suggesting abnormal liver function. LFTs may be requested when a patient:
Newborns: Excessive unconjugated bilirubin damages developing brain cells in infants (kernicterus) and may cause mental retardation, hearing loss, speech difficulties or fits. It is important that bilirubin concentrations in newborns do not get too high. When the concentration of unconjugated bilirubin is greater than 15 times the upper limit of normal, special treatment is used to reduce it: exposure of the skin to blue light and sometimes exchange blood transfusion.
An excessive unconjugated bilirubin concentration may result from the breakdown of red blood cells due to blood typing incompatibility between the mother and her infant. For example, if the mother is Rhesus negative and the foetus inherits the father’s Rhesus positive trait, foetal red blood cells may cross the placenta into the mother’s blood and she may develop antibodies which cross back into the foetus and cause haemolysis of the foetal Rh-positive red blood cells, resulting in excessively elevated unconjugated bilirubin.
Determining conjugated and unconjugated bilirubin concentrations in newborns with jaundice is standard medical care. Malformation of the bile ducts (biliary atresia) obstructs the flow of bile, damaging the liver and causing raised concentrations of conjugated bilirubin. The condition requires early surgical treatment to avoid the need for liver transplantation.
Although unconjugated bilirubin may be toxic to brain development in newborns (up to the age of about 2–4 weeks), high bilirubin concentrations 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 in children or adults, however, strongly suggests a medical condition that must be investigated and treated.
Bilirubin is not normally present in the urine. However, conjugated bilirubin is water-soluble and therefore may be excreted from the body in the urine when concentrations increase in the blood. Its presence in the urine usually indicates blockage of liver or bile ducts, hepatitis or some other liver damage. The most common method for detecting urine bilirubin is using the dipstick test that is part of urinalysis.
This article was last reviewed on 22 March 2016. | This article was last modified on 22 March 2016.
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