What are the delta total serum bilirubin (ΔTSB) thresholds in the new Canadian Paediatric Society hyperbilirubinemia guidelines for term (≥38 weeks) and late‑preterm (35‑37 weeks) infants, and when is phototherapy indicated?

Delta Thresholds and Phototherapy Indications for Neonatal Hyperbilirubinemia

Critical Clarification: No Canadian Paediatric Society Delta Thresholds in Current Evidence

The evidence provided does not contain specific Canadian Paediatric Society (CPS) guidelines with delta total serum bilirubin (ΔTSB) thresholds. The available guidelines are exclusively from the American Academy of Pediatrics (AAP), which uses hour-specific absolute TSB thresholds rather than delta (rate-of-rise) thresholds for phototherapy initiation 1, 2.

When Phototherapy Is Indicated: AAP Hour-Specific Thresholds

For Term Infants (≥38 weeks gestation)

• Phototherapy thresholds are approximately 12–15 mg/dL at 24–48 hours of life and 15–18 mg/dL at ≥72 hours for infants without risk factors 2.
• These are hour-specific values that vary dramatically based on the infant's age in hours, with thresholds being lowest in the first 24-48 hours when neurotoxicity risk is highest 2.

For Late-Preterm Infants (35–37 weeks gestation)

• Phototherapy thresholds are roughly 2–3 mg/dL lower than those for term infants 2.
• Gestational age <38 weeks is itself a neurotoxicity risk factor that mandates lower treatment thresholds 2, 3.

Additional Risk Factors Requiring Lower Thresholds

• Neurotoxicity risk modifiers (sepsis, metabolic acidosis, serum albumin <3.0 g/dL, lethargy, temperature instability) mandate a lower treatment threshold 2.
• Isoimmune hemolytic disease (positive direct antiglobulin test, ABO incompatibility, Rh disease) necessitates earlier phototherapy initiation 2.
• G6PD deficiency is a recognized high-risk condition requiring lower thresholds 2.

Delta TSB: Used for Hemolysis Detection, Not Phototherapy Initiation

While the AAP does not use ΔTSB thresholds to initiate phototherapy, delta values are critical for identifying ongoing hemolysis:

Rate-of-Rise Assessment

• A bilirubin increase of ≥0.3 mg/dL per hour during the first 24 hours or ≥0.2 mg/dL per hour thereafter signals active hemolysis and warrants urgent evaluation 2, 3.
• This rapid rate of rise is exceptional and suggests the need for more aggressive monitoring and potentially earlier intervention 3.
• Multiple serial measurements should be used to calculate the rate 3.

Clinical Significance of Rapid Rise

• If TSB rises despite intensive phototherapy or rises after an initial decline, this strongly suggests hemolysis and requires G6PD testing and consideration of other hemolytic causes 1, 2, 4.

Phototherapy Discontinuation Thresholds

When to Stop Phototherapy

• Discontinue phototherapy when TSB has declined by 2–4 mg/dL below the hour-specific threshold that prompted treatment initiation 2, 4.
• Alternatively, phototherapy can be stopped when TSB falls below 13–14 mg/dL 2, 4.

Post-Phototherapy Monitoring

• High-risk infants (phototherapy started <48 hours of age, gestational age <38 weeks, or hemolytic disease) require TSB check 8–12 hours after cessation, followed by another measurement the next day 2, 4.
• Standard-risk infants should have follow-up TSB within 1–2 days; transcutaneous bilirubin is acceptable if ≥24 hours have elapsed since phototherapy stopped 2.

Intensive Phototherapy Specifications

Technical Requirements

• Use special blue light (430–490 nm spectrum) with irradiance ≥30 μW/cm²/nm delivered over maximum body surface area 1, 2, 4.
• Position the light source as close as safely possible to maximize irradiance 2.
• 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 2, 3.

Expected Response

• A bilirubin decline of >2 mg/dL within 4–6 hours of initiating phototherapy is expected 2, 3.
• If TSB does not decrease or continues to rise during intensive phototherapy, this strongly suggests hemolysis 1.

Critical Pitfalls to Avoid

• Do not rely on visual assessment alone—TSB or TcB measurement is required 2.
• Do not delay phototherapy initiation while waiting for additional testing in high-risk infants 3.
• Do not use TcB alone for treatment decisions in infants approaching phototherapy thresholds; TSB must be used as the definitive test 3.
• Beyond day 5–7, healthy term infants generally do not require phototherapy even if bilirubin exceeds conventional thresholds, because neurotoxicity risk declines sharply with postnatal age—exceptions include ongoing hemolysis, rapid bilirubin rise, or values approaching exchange-transfusion levels 2.