Bilirubinemia is a condition marked by elevated levels of bilirubin in the blood. In newborns, this appears as jaundice, a yellowing of the skin and the whites of the eyes. The condition is common, affecting an estimated 6 out of every 10 full-term babies, and is a temporary and harmless phase of adjusting to life outside the womb.
The Function of Bilirubin
Bilirubin is a yellow-orange pigment created from the breakdown of red blood cells. Newborns produce bilirubin at more than double the adult rate because they have a higher volume of red blood cells with a shorter lifespan. This breakdown process occurs in the liver and spleen.
This initial, “unconjugated” bilirubin is fat-soluble and cannot be easily removed. It is transported to the liver, where an enzyme called UGT converts it into “conjugated” bilirubin. This conjugated form is water-soluble and can be secreted into bile, then eliminated from the body through stool and urine.
A newborn’s developing liver does not produce enough of the required enzyme to process this high load of bilirubin, with an activity level at only 1% of an adult’s. Additionally, some bilirubin in the intestines can be reabsorbed into the bloodstream, further increasing the liver’s workload. This combination of high production and limited processing capacity causes bilirubin levels to build up, leading to jaundice.
Causes of Elevated Bilirubin in Infants
Physiologic jaundice is the most frequent type, appearing two to four days after birth. It occurs because the baby’s immature liver cannot process bilirubin as quickly as it is produced. This form of jaundice resolves on its own within one to two weeks as the liver matures.
Breastfeeding is associated with two types of jaundice. Breastfeeding jaundice occurs in the first week and is related to insufficient milk intake, which causes fewer bowel movements to excrete bilirubin. Breast milk jaundice appears after the first week and can last for several weeks, as substances in the mother’s milk may interfere with the liver’s ability to process bilirubin.
Pathologic jaundice is caused by an underlying medical issue and appears within the first 24 hours of life. A common cause is a blood type incompatibility between the mother and baby, where the mother’s antibodies attack the baby’s red blood cells, causing rapid breakdown and excess bilirubin release. Other causes include infections, internal bleeding, or certain genetic conditions.
Diagnosis and Monitoring
Diagnosis begins with a visual inspection for jaundice, which starts on the face and progresses down the body. Because visual estimation can be unreliable, especially in babies with darker skin, a more definitive screening tool is used.
A non-invasive test using a transcutaneous bilirubinometer is a common screening tool. The device is pressed against the infant’s forehead or chest to measure skin yellowness by analyzing reflected light. This provides a quick estimate of the bilirubin level without a blood draw.
If the screening is high or other risk factors exist, a total serum bilirubin (TSB) blood test provides a definitive diagnosis. A small blood sample is taken from the baby’s heel, and the results are plotted on a chart that compares the bilirubin level to the baby’s age in hours. This helps doctors determine the severity and need for treatment.
Common Treatment Protocols
The most common treatment for high bilirubin levels is phototherapy. This treatment uses blue-green light that is absorbed by bilirubin in the baby’s skin. The light changes the bilirubin molecules into a water-soluble form that can be excreted in urine and stool without needing to be processed by the liver.
During phototherapy, the infant is placed in a bassinet wearing only a diaper and eye protection. The baby’s position is changed periodically to maximize skin exposure. With intensive phototherapy, bilirubin levels can decline by 1 to 2 mg/dL within four to six hours.
Frequent feeding, every two to three hours, is also part of treatment. Adequate nutrition and hydration promote more frequent bowel movements, helping to eliminate bilirubin. In rare cases where phototherapy is not effective, an exchange transfusion may be performed, where the baby’s blood is replaced with donor blood to rapidly lower bilirubin levels.
Signs of Severe Bilirubinemia
Parents should recognize the signs of severe bilirubinemia that require immediate medical attention. A primary warning sign is jaundice that intensifies or spreads to the baby’s legs and feet. Significant changes in the baby’s behavior are also a concern.
Symptoms indicating dangerously high bilirubin levels include:
- Extreme lethargy or difficulty waking for feedings
- A high-pitched, inconsolable cry
- Poor feeding
- A decreased number of wet or dirty diapers
- Unusual arching of the back or neck
These symptoms could signal acute bilirubin encephalopathy, where bilirubin damages the brain. Prompt treatment is necessary to prevent kernicterus, a rare but serious form of permanent brain damage that can cause cerebral palsy, hearing loss, and developmental delays.