Doctors tell whether newborn jaundice is serious by measuring bilirubin, the yellow substance that builds up in the blood, and comparing the result with the baby’s age in hours. They also consider how early the baby was born, how well the baby feeds, whether bilirubin is rising quickly, and whether illness or other risk factors are present. A skin check alone cannot reliably show how high bilirubin is.
Why do doctors focus on bilirubin levels?
Bilirubin is produced when the body breaks down old red blood cells. Before birth, the placenta helps remove it from the baby’s body. After birth, the baby’s liver takes over this job, and it may need time to work efficiently. As a result, yellowing of the skin and the whites of the eyes is common during the first several days of life.
Most newborn jaundice improves without causing problems. However, a very high bilirubin level can affect the brain and lead to serious complications if it is not treated promptly. MedlinePlus explains that healthcare professionals measure bilirubin to identify babies who may need closer monitoring or treatment. The amount of yellow color visible on a baby’s skin does not reliably reveal the bilirubin level, so testing is important when jaundice is suspected.
How do doctors test a newborn for jaundice?
1. Physical examination
A doctor, midwife, or nurse examines the baby’s skin and the whites of the eyes for yellowing. They also consider when the yellow color first appeared and whether it seems to be spreading. The examination provides useful clues, but the appearance alone cannot determine the seriousness of the condition. Yellowing may also be harder to recognize on darker skin, making an objective bilirubin measurement particularly important.
2. A skin bilirubin test
A healthcare professional may use a small handheld device called a transcutaneous bilirubinometer. It shines light through the skin and estimates the bilirubin level by measuring the light reflected back. The test is quick and does not require a blood sample. According to Mayo Clinic, this skin measurement is one of the methods used to assess newborn jaundice. If the result is high or close to a treatment threshold, a blood test may be needed to obtain a more definitive measurement.
3. A blood bilirubin test
A blood test measures bilirubin directly in the baby’s blood. This is commonly called a total serum bilirubin test. A small sample may be collected by gently pricking the baby’s heel. The result helps the healthcare team decide whether the baby needs another measurement, closer observation, or treatment. Under the American Academy of Pediatrics clinical guideline, the blood bilirubin result is the definitive measurement for decisions about phototherapy and escalation of care.
Why does the baby’s age in hours matter?
A bilirubin result cannot be interpreted accurately without knowing the baby’s exact age when the sample was taken. A level that may be expected at one age can be more concerning in a younger newborn. Doctors therefore compare the measured level with age-specific treatment thresholds rather than relying on a single number for all babies.
Gestational age also matters. Babies born earlier may need closer monitoring because their bodies are less mature. Doctors consider the baby’s age in hours, weeks of pregnancy at birth, bilirubin measurement, and factors that increase the risk of bilirubin affecting the brain. The treatment thresholds are adjusted for these differences.
The American Academy of Pediatrics guideline also identifies jaundice during the first 24 hours after birth and a rapid rise in bilirubin as reasons for particular concern. Jaundice appearing during the first day requires prompt measurement and assessment rather than waiting to see whether it improves on its own.
What other factors make doctors more concerned?
The bilirubin level is only part of the assessment. Doctors also review the pregnancy, delivery, feeding history, family history, and the baby’s overall health. Factors that may prompt closer monitoring or additional testing include:
- Premature birth: Babies born before their due date may have greater difficulty processing bilirubin.
- Jaundice during the first 24 hours: Early yellowing can be associated with an underlying problem that needs prompt investigation.
- Rapidly increasing bilirubin: A faster-than-expected rise may suggest that bilirubin is being produced faster than the body can remove it.
- Blood group incompatibility or red blood cell disorders: These can cause red blood cells to break down more quickly. Doctors may consider conditions such as glucose-6-phosphate dehydrogenase deficiency, also called G6PD deficiency.
- Significant bruising: Bruising or a collection of blood under the scalp after delivery can contribute to bilirubin production as the blood is broken down.
- Feeding difficulties: If a baby is not taking in enough milk, bilirubin may build up. Doctors assess feeding, weight changes, urine output, and bowel movements.
- Infection or other illness: A baby who is medically unwell may require closer monitoring and a broader assessment.
These factors do not automatically mean that a baby will develop serious jaundice. Their importance depends on the bilirubin result and the baby’s overall clinical condition. Several factors may be present together, so the healthcare team considers the complete picture rather than one isolated finding.
Which signs may suggest that jaundice needs urgent attention?
The way a baby looks and behaves helps doctors decide how quickly an assessment is needed. Some signs may occur when bilirubin is rising, while others can indicate that the baby is unwell or that the jaundice may have another cause. Examples that deserve prompt attention include:
- Yellowing that appears during the first 24 hours after birth.
- Yellowing that becomes more pronounced or spreads across the body.
- Difficulty waking the baby or unusual sleepiness.
- Feeding poorly or refusing feeds.
- Unusually pale or cream-colored stools, or dark yellow or brown urine.
- Unusual floppiness or stiffness, or jerking movements.
These signs are not a reliable way to estimate the bilirubin level at home. They help identify situations in which medical assessment should not be delayed. The UK National Health Service (NHS) advises urgent medical attention for concerning newborn jaundice and immediate emergency assessment when a jaundiced baby is difficult to wake, is not feeding, has abnormal muscle tone or jerking movements, or has breathing difficulties. A temperature of 38°C or higher, or 36°C or lower, is also a reason for immediate medical attention in a newborn.
Jaundice in a baby younger than 24 hours needs immediate medical assessment. If the baby has any of the concerning signs above, seek urgent medical care rather than waiting for a routine appointment. Pale stools and dark urine should also be reported promptly because they can point to a problem that requires investigation beyond ordinary newborn jaundice.
What happens if the test results are concerning?
The next step depends on the bilirubin level, how quickly it is changing, the baby’s age, and any additional risk factors. A baby whose result is below the treatment threshold may need repeat measurements and a planned follow-up visit. If the level reaches the treatment threshold, the healthcare team may recommend phototherapy, a treatment that uses special light to help the body remove bilirubin.
If the bilirubin level is especially high or rising rapidly, the baby may need hospital care and more intensive monitoring or treatment. Doctors also assess whether an underlying problem is contributing to the jaundice, rather than focusing on the number alone.
Depending on the findings, additional tests may investigate blood group incompatibility, increased breakdown of red blood cells, an inherited red blood cell condition, infection, or a liver or bile-flow problem. MedlinePlus’ information on bilirubin blood tests explains that further testing may be necessary when results or other findings suggest an underlying cause. Not every baby with jaundice needs all these tests; the choice depends on the individual assessment.
Why is follow-up important after the baby goes home?
Bilirubin can continue to rise after birth, so a reassuring assessment at one point does not necessarily mean that no further checks will be needed. Before discharge, the healthcare team reviews the bilirubin result and determines when the baby should be checked again. The timing depends on the measured level in relation to the treatment threshold, the baby’s age, and relevant risk factors.
The American Academy of Pediatrics’ guidance on newborn jaundice recommends measuring bilirubin at least once before discharge for newborns covered by its guideline and using the result to guide follow-up and any repeat testing. Parents should know when the next appointment or test is due and how to contact their healthcare team if feeding becomes difficult or the baby’s condition changes.
In practical terms, doctors judge newborn jaundice by combining an objective bilirubin measurement with the baby’s age, gestational age, health, feeding, and changes over time. This approach helps them distinguish babies who need observation and follow-up from those who need prompt treatment.