Bilirubin is a substance measured in newborns, and its presence causes jaundice, the yellowing of the skin and eyes. This condition affects over half of all term newborns but is typically a harmless, temporary phase. Monitoring bilirubin levels is necessary because while the condition is usually benign, levels must not become excessively high. Assessing these levels allows medical professionals to intervene only when appropriate care is needed.
The Origin of Bilirubin in Newborns
Bilirubin is a waste product created when the body recycles old red blood cells. When red blood cells break down, the hemoglobin’s heme component is converted first into biliverdin and then into bilirubin. This initial form is called unconjugated or indirect bilirubin, which is not water-soluble and must be processed by the liver.
The liver chemically alters this indirect bilirubin through conjugation, making it water-soluble so it can be excreted in the stool and urine. Newborns are prone to high levels of unconjugated bilirubin because they have a higher rate of red blood cell breakdown and their liver enzymes are immature. This temporary imbalance is often referred to as physiological jaundice, and the unconjugated form is monitored because it can be toxic to the developing nervous system.
Understanding Safe Bilirubin Levels
There is no single “good” bilirubin number for a newborn; the safety of a level depends on the baby’s age in hours. Clinicians use charts called nomograms to plot the total serum bilirubin (TSB) level, measured in milligrams per deciliter (mg/dL), against the baby’s age in hours. For example, a level of 10 mg/dL might be acceptable at 72 hours of life but concerning if measured at 12 hours.
These nomograms divide the risk into zones that dictate the need for monitoring or intervention. For a healthy, full-term baby, levels typically peak between three and five days after birth. A level below 6 mg/dL in the first 24 hours is generally expected. A peak level remaining below 15 mg/dL after 72 hours often resolves naturally. The level that prompts action is always assessed considering the baby’s gestational age and the presence of other risk factors.
Screening and Testing for Jaundice
Monitoring bilirubin begins with a visual assessment, followed by objective measurements. The first screening method is often a transcutaneous bilirubin (TcB) measurement, a non-invasive test using a small device placed on the baby’s skin, typically the forehead or sternum. This TcB screening provides a quick estimate of the bilirubin level.
If the TcB reading is high or if the baby has specific risk factors, a blood test is required to confirm the level. This heel-prick procedure measures the total serum bilirubin (TSB), which is the standard for accuracy. Testing is routinely performed before hospital discharge. A follow-up test is usually scheduled within two to three days to capture the peak bilirubin level after the baby leaves the hospital.
Treating High Bilirubin Levels
The goal of treating high bilirubin levels is to prevent kernicterus, a type of brain damage. The most common intervention is phototherapy, or light therapy, which is the first option for treatment. Phototherapy works by exposing the baby’s skin to blue-green light, typically in the 460 to 490 nanometer range.
This light penetrates the skin and changes the unconjugated bilirubin into water-soluble forms called photoisomers. These new forms are easily excreted in the bile and urine without requiring the liver to process them, bypassing the immature conjugation pathway. During treatment, the baby is undressed to maximize skin exposure, and their eyes are shielded to protect the retina. Consistent feeding is also encouraged, as it helps move bilirubin out of the body through the stool. In rare cases where phototherapy is insufficient, an exchange transfusion—replacing the baby’s blood with donor blood—may be necessary to rapidly lower the bilirubin level.
Specific Risk Factors for Severe Jaundice
Several specific factors increase a newborn’s risk of developing high bilirubin levels. Prematurity is a primary factor, as babies born before 37 weeks have less mature livers and are more susceptible to bilirubin toxicity.
- Blood group incompatibility, such as Rh or ABO incompatibility between the mother and baby, can lead to rapid destruction of the baby’s red blood cells, causing a high bilirubin load.
- Significant bruising or a collection of blood under the scalp (cephalohematoma) contributes by increasing the amount of red blood cells breaking down.
- Genetic factors, such as glucose-6-phosphate dehydrogenase (G6PD) deficiency, impair red blood cell survival.
- Poor feeding, resulting in excessive weight loss or dehydration, can increase the reabsorption of bilirubin from the intestines, leading to higher serum levels.