A bilirubin nomogram is a specialized chart used by healthcare professionals to assess the risk of severe jaundice in newborns. Bilirubin, a yellow pigment from red blood cell breakdown, can cause jaundice (yellowing of skin and eyes) at high levels. The nomogram provides a visual representation of bilirubin levels relative to a baby’s age in hours, aiding in proactive management.
How to Read a Bilirubin Nomogram
Reading a bilirubin nomogram involves locating two specific pieces of information to plot a point. The horizontal axis (x-axis) represents the infant’s age in hours since birth, typically ranging from 0 to 120 hours or more. The vertical axis (y-axis) shows the total serum bilirubin (TSB) level, usually measured in milligrams per deciliter (mg/dL).
To plot a point, a healthcare provider first finds the baby’s exact age in hours on the horizontal axis. From that point, they move vertically up the chart until aligning with the baby’s measured TSB level on the vertical axis. The intersection of these two lines marks the baby’s current bilirubin status on the nomogram. For instance, a baby 48 hours old with a bilirubin level of 8 mg/dL would have a point plotted by finding 48 on the x-axis and 8 on the y-axis, then marking their intersection.
Understanding the Risk Zones
The most widely recognized bilirubin nomogram is the Bhutani nomogram, which divides the chart into distinct risk zones using percentile lines. These lines delineate areas of high, high-intermediate, low-intermediate, and low risk for developing severe hyperbilirubinemia, defined as bilirubin levels exceeding the 95th percentile for their age in hours.
A baby whose plotted point falls into the high-risk zone has a considerable likelihood of bilirubin levels increasing to a range that could necessitate intervention. The high-intermediate risk zone suggests a moderate likelihood of reaching concerning bilirubin levels, warranting close observation. Conversely, the low-intermediate risk zone indicates a lower, but still present, likelihood, while the low-risk zone suggests a minimal likelihood of developing severe hyperbilirubinemia.
Clinical Significance and Follow-Up
The primary purpose of using a bilirubin nomogram is to prevent kernicterus, a rare but serious type of brain damage that can result from very high, untreated bilirubin levels. By identifying infants at risk early, healthcare providers can proactively manage jaundice and potentially avert this severe neurological injury. The nomogram helps guide decisions about monitoring and care, tailoring the approach to each infant’s specific risk profile.
Follow-up actions are determined by which risk zone the baby’s bilirubin level falls into. Infants in the low-risk zone may not require further immediate action, though parents are often counseled on signs of worsening jaundice. Babies in the intermediate-risk zones typically need repeat bilirubin testing within a specified timeframe, such as 24 to 48 hours, to monitor the trend of their bilirubin levels. For infants whose levels are in the high-risk zone, interventions like phototherapy are often considered to help reduce bilirubin levels.