Newborn Jaundice Bilirubin Levels: What Do the Numbers Mean?

A newborn bilirubin level shows how much bilirubin, the yellow substance that causes jaundice, is in the baby's blood or skin. There is no single safe number for every baby: clinicians compare the result with the baby's age in hours, how many weeks pregnant the birth was, and any risk factors, using a treatment threshold chart.

Newborn jaundice is common and usually harmless. The NHS explains that it is usually most noticeable around day 3 and usually takes about 2 weeks to go. This guide helps parents understand the numbers and charts they may hear about. It cannot tell you whether your baby needs treatment; only the team caring for your baby can decide that.

Do not wait for a planned blood test or a callback if your baby has any of the signs below. The NHS advises calling the emergency number or going to an emergency department for these signs. In the UK, that means 999 or A&E. Elsewhere, use your local emergency number.

Same-day help: The NHS advises asking for an urgent appointment or calling NHS 111 if you think your baby (over 24 hours old) has jaundice, if the yellow colour is not improving or is getting worse, or if their pee is dark yellow or brown or their poo is a pale creamy colour. Pale, chalky stools can point to a liver or bile problem and should always be reported, even if the jaundice looks mild.

The American Academy of Pediatrics (AAP) also advises calling the doctor if the skin is getting more yellow, the tummy, arms or legs look yellow, the whites of the eyes are yellow, or the baby is hard to wake, fussy, or not feeding well.

• Jaundice in a baby less than 24 hours old.
• Sleepier than normal or difficult to wake.
• Not feeding, or feeding much less than usual.
• Floppy or stiff, or jerking or twitching movements.
• A high temperature, or a low temperature, or difficulty breathing.
• No wet nappies (diapers).

In the first days of life, bilirubin normally rises and then falls. A level that would be expected at day 4 might be a concern at 20 hours old. For this reason, the result only makes sense next to the baby's exact age in hours when the sample was taken.

UK guidance based on NICE asks staff to plot every serum bilirubin result by the hour of sampling on a phototherapy chart. One NHS neonatal guideline stresses that treatment thresholds vary with gestation and age after birth, so accurate plotting is vital. In the US, the 2022 AAP guideline uses threshold figures that depend on gestational age and on whether the baby has extra risk factors.

This is why two babies with the same number can be managed differently. If you are told a level, ask what age in hours it was taken at and where it sits on the chart.

A treatment threshold chart has the baby's age in hours along the bottom and the bilirubin level up the side. Lines on the chart show where clinicians would start phototherapy and, at much higher levels, consider more intensive treatment. Different charts or lines are used for different gestations.

Under the 2022 AAP guideline, babies born before 38 weeks are treated as having a risk factor, and a separate set of lines is used when there are other risk factors too. A review of the AAP update notes that the phototherapy and exchange thresholds were raised compared with earlier guidance, partly because phototherapy can have downsides of its own.

We have not reproduced chart numbers here. The thresholds differ between countries, gestations and guideline versions, and units differ too: the UK uses micromoles per litre, while the US uses milligrams per decilitre. Your baby's team will use the chart that applies locally.

Looking at the skin is not a reliable way to judge how high bilirubin is, and jaundice can be harder to see on black or brown skin. Teams measure it instead, either with a small device pressed against the skin (a transcutaneous bilirubinometer) or with a blood test, often from a heel prick.

Skin readings are useful for screening, but high readings are confirmed with a blood test. UK guidance says a blood test is needed for babies under 24 hours old with visible jaundice and for babies born before 35 weeks. The AAP advises that every baby has at least one bilirubin check before leaving hospital, and that babies discharged before 48 hours are usually seen again within 2 days.

If jaundice is unusual, early, or lasting, the team may add tests such as a blood count, a Coombs test for antibodies, a reticulocyte count or a split bilirubin to look at the conjugated part, which relates to the liver.

Phototherapy uses light on the baby's skin to help break down bilirubin so the body can clear it. Babies usually lie in a cot or incubator wearing only a nappy, often with eye shields. The NHS says most babies need about 48 hours, and it is usually given in hospital, though some families can use equipment at home.

Feeding continues during phototherapy. Frequent feeds, around 8 to 12 times a day according to the NHS and AAP, help the baby pass bilirubin in their stools. Sunlight is not a safe treatment. Rarely, very high levels need an exchange transfusion or an intravenous medicine in hospital. Very high bilirubin can, rarely, harm the brain (kernicterus), which is why checks and treatment matter.

MedlinePlus notes that most newborn jaundice clears within 1 to 2 weeks. Breastfed babies sometimes stay mildly yellow for longer. The AAP suggests checking with the doctor if jaundice lasts beyond 2 weeks in formula-fed babies or beyond 4 weeks in breastfed babies, while UK practice reviews term babies who are still visibly jaundiced after 14 days. Follow your local team's advice and report pale stools or dark urine at any age.

Write down the answers, or ask for a copy of the chart, so you have them at the next check.

• What was my baby's bilirubin level, how was it measured, and how many hours old were they?
• Where does the level sit on the treatment chart, and how close is it to the treatment line?
• Does my baby have any risk factors that change which chart or line you use?
• When is the next check, and who will contact me with the result?
• Which signs should make me call straight away rather than wait?

On SameCase, parents can read de-identified cases from other families and see how verified doctors discussed similar situations, such as a level close to a treatment line. This can help you think of questions for your baby's team. It cannot tell you what your baby's result means or replace urgent care.