Kernicterus risk is associated with bilirubin levels exceeding what value?

• A. >20 mg/dL
• B. >5 mg/dL
• C. >10 mg/dL
• D. >2 mg/dL

Answer: (A)

High levels of unconjugated bilirubin in a newborn can cross the immature blood–brain barrier and deposit in brain tissue, leading to bilirubin-induced neurologic damage (kernicterus). As bilirubin rises and the binding capacity of albumin becomes overwhelmed, more bilirubin remains free to enter the CNS, increasing the risk of injury. In term infants, this risk becomes notably significant when total serum bilirubin exceeds about 20 mg/dL, which is why this threshold is often used to guide urgent treatment decisions like intensified phototherapy or exchange transfusion. Remember, kernicterus is linked to unconjugated bilirubin, not the direct (conjugated) fraction, which does not cross into brain tissue in the same way.