Bilirubin is a byproduct of red blood cell breakdown. The “bilirubin curve” is a tool used to track bilirubin levels. It helps in understanding if bilirubin levels are within a healthy range, particularly in newborns. This tracking is important because elevated levels can sometimes indicate a need for medical attention.
Bilirubin Basics
Bilirubin originates from the breakdown of hemoglobin, a protein found in red blood cells. When red blood cells break down, primarily in the spleen and liver, heme converts to biliverdin, then to unconjugated bilirubin. This unconjugated bilirubin is not water-soluble and binds to albumin in the bloodstream. In the liver, unconjugated bilirubin is “conjugated,” becoming water-soluble for excretion in bile, leaving the body via stool and urine. A buildup of bilirubin, known as hyperbilirubinemia, can lead to jaundice, which is characterized by a yellowish discoloration of the skin and eyes.
Mapping Bilirubin Levels
The bilirubin curve, or nomogram, plots an infant’s bilirubin levels against their age in hours. This visual representation helps healthcare professionals assess the risk of a newborn developing severe hyperbilirubinemia, a condition where bilirubin levels become excessively high. By plotting a baby’s total serum bilirubin (TSB) or transcutaneous bilirubin (TcB) measurement on the nomogram, providers can determine if the levels are rising too quickly or reaching dangerous thresholds.
This curve is designed for infants born at 35 or more weeks of gestation. It provides a standardized way to interpret bilirubin levels, considering that what might be a normal level at one age could be concerning at another. The nomogram guides healthcare decisions on further monitoring, additional testing, or treatment to prevent potential complications. Using this hour-specific approach is more accurate than simply considering the infant’s age in days, as even small differences in age can significantly impact risk assessment.
Understanding the Risk Zones
The bilirubin curve has distinct zones, each indicating a different risk level for severe hyperbilirubinemia. These zones include low-risk, intermediate-low risk, intermediate-high risk, and high-risk categories. The placement of an infant’s bilirubin level on this curve, in relation to their age in hours, helps predict the likelihood of their bilirubin levels exceeding the 95th percentile, which defines the high-risk zone.
A bilirubin level falling within the low-risk zone suggests a very low chance of developing severe hyperbilirubinemia. Conversely, a high-risk zone level indicates a high probability of severe hyperbilirubinemia, requiring close monitoring and intervention. Intermediate zone levels warrant careful observation and more frequent bilirubin measurements. The trend of the bilirubin level, whether it is rapidly rising or plateauing, also influences the interpretation of risk and subsequent clinical decisions.
Treating Elevated Bilirubin
When bilirubin levels are elevated into higher-risk zones, interventions prevent complications. Phototherapy is a common treatment for neonatal jaundice. This therapy exposes the infant’s skin to specific blue-green light wavelengths (420-550 nanometers). The light converts the unconjugated bilirubin molecules in the skin into water-soluble isomers that can be easily excreted from the body through urine and stool without further processing by the liver.
For severe cases where phototherapy is insufficient or acute bilirubin encephalopathy signs appear, an exchange transfusion may be necessary. This procedure removes small amounts of infant blood while simultaneously replacing it with donor blood. The primary goal of an exchange transfusion is to rapidly reduce circulating bilirubin levels and remove antibody-coated red blood cells, thus preventing serious neurological damage such as kernicterus.