What are the Canadian Paediatric Society (CPS) guideline delta thresholds for initiating phototherapy in neonatal hyperbilirubinemia for low‑risk, moderate‑risk, and high‑risk infants?

Canadian Paediatric Society Phototherapy Thresholds for Neonatal Hyperbilirubinemia

The Canadian Paediatric Society does not use "delta thresholds" (rate-of-rise values) to initiate phototherapy—instead, they follow the American Academy of Pediatrics approach of using hour-specific absolute total serum bilirubin (TSB) thresholds based on gestational age and neurotoxicity risk factors. 1

Understanding the Threshold System

The phototherapy decision is based on absolute TSB levels plotted against the infant's age in hours, not on how fast the bilirubin is rising. 1 The thresholds vary dramatically in the first days of life and are stratified by risk category:

Risk-Based Phototherapy Thresholds

Low-Risk Infants (≥38 weeks gestation, no risk factors):

• At 24-48 hours of life: approximately 12-15 mg/dL (205-257 µmol/L) 1
• At ≥72 hours of life: approximately 15-18 mg/dL (257-308 µmol/L) 1

Moderate-Risk Infants (35-37 6/7 weeks gestation OR presence of any neurotoxicity risk factor):

• Thresholds are roughly 2-3 mg/dL (34-51 µmol/L) lower than low-risk infants at corresponding ages 1

High-Risk Infants (multiple risk factors, isoimmune hemolytic disease, G6PD deficiency):

• Even lower thresholds apply, requiring individualized assessment using hour-specific nomograms 1

Neurotoxicity Risk Factors That Lower Thresholds

• Gestational age <38 weeks (especially 35-37 6/7 weeks) 1
• Sepsis or clinical instability 1
• Metabolic acidosis 1
• Serum albumin <3.0 g/dL 1
• Lethargy or temperature instability 1
• Isoimmune hemolytic disease (positive DAT, ABO/Rh incompatibility) 1
• G6PD deficiency 1

When Rate-of-Rise Matters (But Doesn't Set Thresholds)

While delta values don't determine when to start phototherapy, a rapid rate of rise signals active hemolysis and warrants urgent evaluation:

• ≥0.3 mg/dL per hour in the first 24 hours 2, 1
• ≥0.2 mg/dL per hour after 24 hours 2, 1

These rates indicate ongoing hemolysis and should prompt G6PD testing and closer monitoring, but phototherapy initiation still depends on absolute TSB crossing the hour-specific threshold, not the rate alone. 1

Critical Age-Related Context

Beyond day 5-7 of life in healthy term infants, phototherapy is generally not indicated even if bilirubin exceeds typical thresholds, because neurotoxicity risk diminishes substantially with postnatal age. 1 Exceptions include:

• Ongoing hemolytic disease 1
• Rapid bilirubin rise despite age 1
• TSB approaching exchange transfusion levels (≥25 mg/dL or 428 µmol/L) 1
• Signs of acute bilirubin encephalopathy 1

Practical Implementation

Obtain a confirmatory TSB when transcutaneous bilirubin (TcB) is within 3 mg/dL (51 µmol/L) of the phototherapy threshold, exceeds the threshold, or is ≥15 mg/dL (257 µmol/L). 1 Visual assessment alone is unreliable and should never guide treatment decisions. 1

If TSB crosses the hour-specific threshold for the infant's risk category, initiate intensive phototherapy immediately using blue light (430-490 nm) with irradiance ≥30 μW/cm²/nm. 1, 3

Common Pitfall to Avoid

Do not confuse the rate-of-rise criteria (0.2-0.3 mg/dL per hour) with phototherapy initiation thresholds—these delta values are diagnostic indicators of hemolysis, not treatment triggers. 2, 1 The decision to start phototherapy must be based on absolute TSB plotted on hour-specific nomograms. 1