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If your baby has prolonged jaundice, they might be referred for a split bilirubin blood test. Here we talk about the test and what the results might mean.

Why does my baby need a split bilirubin blood test?

If your baby’s had prolonged jaundice, they should have a split bilirubin blood test (CLDF, 2018). The split bilirubin test checks your baby’s blood for the ratio of conjugated and unconjugated bilirubin. This test will help to check whether your baby’s jaundice is caused by an underlying condition like liver disease (CLDF, 2018; Lab Tests Online, 2018).

What is unconjugated and conjugated bilirubin?

Bilirubin is the yellowy orange substance we all produce during as we break down the haem part of the haemoglobin from our red blood cells. We change haem into unconjugated bilirubin (not water-soluble) and our livers change that unconjugated bilirubin into conjugated bilirubin (water-soluble). This conjugated bilirubin is a waste product that goes into our bile, then the intestine; it’s this broken down bilirubin in bile that gives poo its brown colour (Lab Tests Online, 2018).

If your baby has a blockage or inflammation in their liver or their biliary drainage system, the bile might stop draining from their liver. This will mean their poo will look pale (CLDF, 2015). That’s why it’s important to check the colour of your baby’s poos against this chart.

What is normal for the split bilirubin test?

It’s usual for the blood to contain small amounts of unconjugated bilirubin but almost no conjugated bilirubin (Lab Tests Online, 2018)

Results that might indicate a problem

1. High levels of unconjugated bilirubin (unconjugated hyperbilirubinaemia)

Treatment for high levels of unconjugated bilirubin may be necessary because in rare cases it could cause brain damage (kernicterus) (NHS, 2018).

2. Presence of conjugated bilirubin (conjugated hyperbilirubinaemia)

If your baby’s conjugated bilirubin is more than 20% of the total bilirubin, this suggests they have liver disease. A specialist paediatric liver unit will further investigate your baby’s condition (CLDF, 2018).

Treatment for high levels of unconjugated bilirubin (unconjugated hyperbilirubinaemia)

Most babies will not need any treatment as their jaundice will have gone by the time they’re two weeks old (or three weeks if premature). A few babies will have to have some treatment, depending on how much bilirubin they have in their blood (NHS, 2018).

The normal treatment for prolonged jaundice is phototherapy, which reduces bilirubin levels. If your baby needs this, they’ll be placed naked, except for some eye pads, in a cot under a special blue light. You will be encouraged to feed your baby so your baby produces plenty of wee. Phototherapy usually continues for a few days (NHS, 2018).

How is jaundice due to raised conjugated bilirubin different to that from raised unconjugated bilirubin?

Unlike unconjugated bilirubin, phototherapy does not break down conjugated bilirubin.

On the other hand, conjugated bilirubin can’t pass into the brain so it will not damage the brain (very high levels of unconjugated bilirubin can) (CLDF, 2015).

Conjugated bilirubin can dissolve in water so some of it gets into wee and makes it yellow. Yet poo might be paler because it contains less bile (CLDF, 2015).

If your baby has raised conjugated bilirubin, they’ll have more fats in their poo because they don’t have as much bile to digest fats. This will make your baby particularly hungry and they might have difficulty gaining the usual amount of weight as they get older. Their liver might also be larger than usual because of the inflammation and swelling from the trapped bile (CLDF, 2015).

How will my baby’s raised conjugated bilirubin (hyperbilirubinaemia) be investigated?

Your local hospital or a specialist centre might investigate why your baby has raised conjugated bilirubin and whether they need any special treatment (CLDF, 2015). Your baby might have the following investigations:

  • an examination by a doctor
  • blood tests
  • urine tests
  • stool examination or tests
  • an ultrasound scan
  • specialised scans
  • a liver biopsy
  • X-ray
  • an eye test
  • a heart test
  • a bone marrow test.

(CLDF, 2015)

What usually causes conjugated hyperbilirubinaemia?

While conjugated jaundice can be caused by a lot of different things, these causes can be grouped into the following:

  • Bile duct drainage issues mean that the bile ducts have an abnormality. One such condition is biliary atresia, which is where bile ducts outside of the liver collapse or disappear and obstruct bile flow.
  • Metabolic conditions mean liver cells have an abnormality in how they make or pass out bile, or in how they metabolise nutrients from your baby’s milk.
  • Unknown. Up to a third of all babies who test positive for raised conjugated bilirubin do not have a known cause for it. Babies who experienced other medical problems soon after they were born more often have unknown causes of raised conjugated bilirubin.

(CLDF, 2015)

Treatment for conjugated hyperbilirubinaemia

Your baby might need special feeds and medication to help them deal with poor bile flow until it improves (CLDF, 2015).

Doctors might start treatments like:

  • a special diet
  • medication
  • an operation.

(CLDF, 2015)

Is conjugated hyperbilirubinaemia serious?

This depends on why your baby has conjugated hyperbilirubinaemia, because conjugated bilirubin on its own is not serious (CLDF, 2015).

If doctors can’t identify a cause, your baby is likely progress well, with their jaundice gradually clearing over weeks (or months) with no long-term ill effect. Some children will continue to have ongoing liver problems and will need further treatment. That’s why all babies with high levels of conjugated bilirubin are followed up (CLDF, 2015).

If your baby has prolonged jaundice that isn’t getting better, has very pale poo or you are concerned about your baby’s health, it’s important to contact your GP as soon as possible.

This page was last reviewed in May 2018.

Further information

Our support line offers practical and emotional support with feeding your baby and general enquiries for parents, members and volunteers: 0300 330 0700.

NHS Choices and the Children’s Liver Disease Foundation have more information about newborn jaundice and liver disease in babies.

The Children’s Liver Disease Foundation is dedicated to fighting all forms of childhood liver disease. Their Yellow Alert campaign promotes the early diagnosis of liver disease in newborns. 

CLDF (Children’s Liver Disease Foundation). (2015) Baby jaundice and liver disease. Available at: [Accessed 8th May 2018].

CLDF (Children’s Liver Disease Foundation). (2018) Baby jaundice. Available at: [Accessed 8th May 2018].

Lab Tests Online (2018) Bilirubin. Available at: [Accessed 8th May 2018].

NHS. (2018) Newborn jaundice. Available at: [Accessed 8th May 2018].


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