What is the next step in managing an infant's bilirubin levels given a decrease in Transcutaneous Bilirubin (TcB)?

Management of Decreased Transcutaneous Bilirubin (TcB)

When TcB decreases during phototherapy, continue treatment and confirm the decline with a total serum bilirubin (TSB) measurement, as TcB readings are unreliable during and immediately after phototherapy due to skin bleaching effects. 1

Understanding TcB Limitations During Phototherapy

• TcB measurements cannot be trusted during active phototherapy because phototherapy "bleaches" the skin, making both visual assessment and transcutaneous measurements unreliable 1
• TcB readings can underestimate TSB by 2.4 mg/dL (SD 2.1 mg/dL) within the first 8 hours after phototherapy, with the difference gradually returning to baseline over 24 hours 2
• The skin bilirubin decreases rapidly (25% reduction within 2 hours), while serum bilirubin may remain unchanged during the first 4 hours of treatment, creating a significant discrepancy 3

Immediate Actions Required

• Obtain a TSB measurement to verify the actual bilirubin level, as this is the only reliable method to assess treatment response during phototherapy 1, 4
• Timing of TSB testing depends on the initial bilirubin trajectory and infant age: measure TSB within 2-3 hours if initial TSB was ≥25 mg/dL, within 3-4 hours if TSB was 20-25 mg/dL, and within 4-6 hours if TSB was <20 mg/dL 4
• For infants requiring escalation of care (TSB at or within 2 mg/dL of exchange transfusion threshold), measure TSB at least every 2 hours until the escalation period ends 1, 4

Determining When to Continue or Stop Phototherapy

• Continue intensive phototherapy until TSB has declined by 2-4 mg/dL below the hour-specific threshold at which phototherapy was initiated 1, 4
• The decision should account for the initial TSB level, the underlying cause of hyperbilirubinemia (particularly hemolysis), and the risk of rebound hyperbilirubinemia 4
• For extremely high bilirubin levels (>30 mg/dL), expect a decline of up to 10 mg/dL within a few hours and at least 0.5-1 mg/dL per hour in the first 4-8 hours 4

Post-Phototherapy Monitoring Strategy

• High-risk infants (those treated <48 hours of age, gestational age <38 weeks, positive direct antiglobulin test, or suspected hemolytic disease) require TSB measurement 8-12 hours after phototherapy discontinuation and again the following day 1, 4
• Standard-risk infants require follow-up TSB within 1-2 days after phototherapy discontinuation 1, 4
• TcB can be used instead of TSB only if ≥24 hours have passed since phototherapy was stopped, as the skin bleaching effect resolves over this timeframe 1, 4, 2

Critical Pitfalls to Avoid

• Never rely on TcB alone to guide treatment decisions during active phototherapy or within 8 hours of stopping phototherapy, as readings can be falsely low by up to 7.3 mg/dL 1, 2
• Do not assume a decreasing TcB means the infant is adequately responding—serum bilirubin may still be rising despite skin bleaching 3
• Avoid premature discontinuation of phototherapy based solely on TcB readings, as this can lead to rebound hyperbilirubinemia requiring readmission 4

Evaluating for Underlying Hemolysis

• If TSB rises despite intensive phototherapy or rises after an initial decline, measure glucose-6-phosphate dehydrogenase (G6PD) enzyme activity immediately 1, 4
• A rapid rate of rise (≥0.3 mg/dL per hour in the first 24 hours or ≥0.2 mg/dL per hour thereafter) suggests ongoing hemolysis and may warrant IVIG administration (0.5-1 g/kg over 2 hours) in cases of isoimmune hemolytic disease 1, 5
• For infants with documented hemolysis and TSB within 2-3 mg/dL of exchange transfusion threshold despite intensive phototherapy, administer IVIG and consider repeating the dose in 12 hours if necessary 5