At what bilirubin levels is phototherapy required?

Phototherapy Thresholds for Neonatal Hyperbilirubinemia

Phototherapy should be initiated based on hour-specific total serum bilirubin (TSB) thresholds that vary by gestational age, postnatal age in hours, and the presence of neurotoxicity risk factors, as outlined in the American Academy of Pediatrics 2024 guidelines. 1

Key Principle: Use TSB, Not Visual Assessment

• TSB must be used as the definitive diagnostic test to guide all phototherapy decisions—transcutaneous bilirubin (TcB) is adequate for screening but not accurate enough for treatment decisions 1
• TSB should be measured if TcB is within 3.0 mg/dL of the phototherapy threshold, if TcB exceeds the threshold, or if TcB is ≥15 mg/dL 1
• Never rely on visual assessment of jaundice alone 2, 3

Phototherapy Thresholds by Clinical Context

The specific bilirubin level requiring phototherapy depends on three critical factors:

1. Gestational Age at Birth

• Infants ≥38 weeks gestation have higher thresholds than preterm infants 1
• For low birth weight infants (1500-2500g), some older data suggested starting at 12 mg/dL, or 10 mg/dL for infants <1500g 4

2. Postnatal Age in Hours

• Thresholds increase as the infant ages (e.g., 25-48 hours vs 49-72 hours vs >72 hours) 1, 5
• For term infants without risk factors, historical thresholds were approximately 15 mg/dL at 25-48 hours, 18 mg/dL at 49-72 hours, and 20 mg/dL after 72 hours 5

3. Presence of Neurotoxicity Risk Factors

• Risk factors lower the phototherapy threshold and include: positive direct antiglobulin test (DAT), G6PD deficiency, asphyxia, lethargy, temperature instability, sepsis, acidosis, and albumin <3.0 g/dL 1, 2
• Infants with isoimmune hemolytic disease require more aggressive treatment 1

Critical Action Thresholds

Emergency Level: TSB ≥25 mg/dL

• This is a medical emergency requiring immediate admission directly to a hospital pediatric service for intensive phototherapy 1
• Do not refer to the emergency department as this delays treatment 1
• 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 3

Escalation of Care Level: Within 0-2 mg/dL Below Exchange Threshold

• Requires intravenous hydration and emergent intensive phototherapy 1
• TSB should be measured at least every 2 hours until the escalation period ends 1
• Consult neonatology if TSB continues to rise despite intensive phototherapy 1

Identifying Hemolysis (Requires Lower Thresholds)

• A rapid rate of rise is exceptional and suggestive of ongoing hemolysis: ≥0.3 mg/dL per hour in the first 24 hours or ≥0.2 mg/dL per hour thereafter 1, 2
• If TSB does not fall or continues to rise despite intensive phototherapy, hemolysis is very likely occurring 1
• Obtain G6PD testing if bilirubin rises despite phototherapy, rises after initial decline, or requires escalation of care 1, 2

Important Clinical Pitfalls

• Do not subtract direct (conjugated) bilirubin from total bilirubin when making treatment decisions 1, 2, 3
• If direct bilirubin is ≥50% of total bilirubin, consult a specialist as standard guidelines do not apply 1, 2
• For infants ≥13 mg/dL, obtain comprehensive laboratory evaluation including TSB, direct bilirubin, blood type, DAT, albumin, CBC with differential, reticulocyte count, and G6PD if indicated 1, 2

Discontinuing Phototherapy

• Stop phototherapy when TSB has declined by 2-4 mg/dL below the hour-specific threshold at which it was initiated 1, 3
• Alternatively, discontinue when TSB falls below 13-14 mg/dL 2, 3
• For high-risk infants (hemolytic disease, phototherapy <48 hours of age, gestational age <38 weeks, positive DAT), obtain follow-up TSB 8-12 hours after discontinuation and again the following day 1, 3
• For standard-risk infants, obtain follow-up TSB within 1-2 days after discontinuation 1, 3