At what bilirubin level do you start phototherapy?

Bilirubin Thresholds for Initiating Phototherapy in Neonates

Phototherapy should be initiated when total serum bilirubin (TSB) exceeds threshold values based on gestational age, age in hours, and presence of risk factors for bilirubin neurotoxicity, with thresholds of 13-15 mg/dL for high-risk infants, 15-18 mg/dL for medium-risk infants, and 18-20 mg/dL for low-risk infants. 1

Risk-Based Approach to Phototherapy Initiation

The decision to start phototherapy depends on several key factors:

1. Gestational age: Preterm infants have lower thresholds than term infants
2. Postnatal age in hours: Thresholds increase with age
3. Presence of neurotoxicity risk factors: Lower thresholds for infants with risk factors

Risk Categories and Corresponding Thresholds:

• High-risk infants: 13-15 mg/dL
• Medium-risk infants: 15-18 mg/dL
• Low-risk infants: 18-20 mg/dL 1

Diagnostic Testing and Monitoring

• TSB is the definitive diagnostic test for guiding all interventions 2
• Transcutaneous bilirubin (TcB) measurements should be confirmed with TSB if:
  • TcB is within 3.0 mg/dL of phototherapy threshold
  • TcB exceeds phototherapy threshold
  • TcB is ≥15 mg/dL 2
• During phototherapy, TcB measurements are unreliable unless measured on patched skin areas 1

Phototherapy Implementation

For effective phototherapy:

• Use blue-green wavelength light (460-490 nm) with peak at 478 nm 1
• Ensure minimum irradiance of 30 μW·cm⁻²·nm⁻¹ 1
• Maximize body surface area exposure (35-80% of skin) 2, 1
• For severe hyperbilirubinemia (TSB >25 mg/dL), implement "crash-cart" approach with rapid phototherapy to reduce need for exchange transfusion 2

Monitoring During Phototherapy

Frequency of TSB monitoring depends on initial bilirubin levels:

• TSB ≥25 mg/dL: Recheck within 2-3 hours (expect 30-40% decline in 24 hours) 1
• TSB 20-25 mg/dL: Recheck within 3-4 hours (expect 6-20% decline in 24 hours) 1
• **TSB <20 mg/dL**: Recheck in 4-6 hours (expect >2 mg/dL decline in first 4-6 hours) 1
• Escalation of care: Check TSB at least every 2 hours 1

Discontinuation of Phototherapy

• Discontinue when TSB has declined by 2-4 mg/dL below the hour-specific threshold at which phototherapy was initiated 2, 1
• For infants readmitted after birth hospitalization (usually for TSB ≥18 mg/dL), phototherapy may be discontinued when serum bilirubin falls below 13-14 mg/dL 1

Follow-up After Phototherapy

• High-risk infants (phototherapy <48 hours of age, gestational age <38 weeks, positive direct antiglobulin test, or suspected hemolytic disease): Check TSB 8-12 hours after discontinuation and again the following day 2, 1
• Other infants: Check TSB within 1-2 days after discontinuation 2, 1

Common Pitfalls to Avoid

1. Inadequate monitoring frequency in severe hyperbilirubinemia, missing rapid rises in bilirubin levels 1
2. Premature discontinuation of phototherapy leading to rebound hyperbilirubinemia 1
3. Relying on transcutaneous bilirubin during phototherapy without using patched skin areas 1, 3
4. Failing to identify underlying causes of hyperbilirubinemia, particularly when response to therapy is suboptimal 2, 1
5. Not considering potential increases in bilirubin after red blood cell transfusions 4

Special Considerations

• Evaluate for hemolysis if TSB rises rapidly (≥0.3 mg/dL per hour in first 24 hours or ≥0.2 mg/dL per hour thereafter) 2
• Consider home phototherapy with LED-based devices for specific eligible infants rather than hospital readmission 2
• Measure glucose-6-phosphate dehydrogenase enzyme activity in infants with jaundice of unknown cause whose TSB rises despite intensive phototherapy 2

By following these evidence-based guidelines, clinicians can effectively manage neonatal hyperbilirubinemia while minimizing the risk of bilirubin-induced neurological damage.