Bilirubin Level Calculator

Newborn jaundice affects approximately 60% of term infants and 80% of preterm infants.

It occurs when bilirubin—a natural byproduct of red blood cell breakdown—accumulates faster than the immature neonatal liver can process it.

This Bilirubin Level Calculator evaluates total serum bilirubin (TSB) against postnatal age in hours to provide risk stratification, phototherapy proximity, and recommended follow-up intervals based on established Bhutani nomogram guidelines updated for 2026 practice.

The Logic Behind Bilirubin Risk Assessment

Neonatal bilirubin assessment requires plotting total serum bilirubin against exact postnatal age in hours.

The calculator uses the four standard age tiers and corresponding zone cutoffs derived from the Bhutani hour-specific nomogram:

• Under 24 Hours:
  • High Risk: $\ge 10\text{ mg/dL}$
  • High Intermediate: $8.0 - 9.9\text{ mg/dL}$
  • Low Intermediate: $6.0 - 7.9\text{ mg/dL}$
  • Low Risk: $< 6.0\text{ mg/dL}$
• 24 to 47 Hours:
  • High Risk: $\ge 15\text{ mg/dL}$
  • High Intermediate: $13.0 - 14.9\text{ mg/dL}$
  • Low Intermediate: $10.0 - 12.9\text{ mg/dL}$
  • Low Risk: $< 10.0\text{ mg/dL}$
• 48 to 71 Hours:
  • High Risk: $\ge 18\text{ mg/dL}$
  • High Intermediate: $15.0 - 17.9\text{ mg/dL}$
  • Low Intermediate: $12.0 - 14.9\text{ mg/dL}$
  • Low Risk: $< 12.0\text{ mg/dL}$
• 72+ Hours:
  • High Risk: $\ge 20\text{ mg/dL}$
  • High Intermediate: $17.0 - 19.9\text{ mg/dL}$
  • Low Intermediate: $14.0 - 16.9\text{ mg/dL}$
  • Low Risk: $< 14.0\text{ mg/dL}$

Treatment Threshold Formulas

$$\text{Phototherapy Threshold (mg/dL)} = \begin{cases} 10 & \text{if } \text{Age} < 24\text{ h} \ 15 & \text{if } 24 \le \text{Age} < 48\text{ h} \ 18 & \text{if } 48 \le \text{Age} < 72\text{ h} \ 20 & \text{if } \text{Age} \ge 72\text{ h} \end{cases}$$

$$\text{Exchange Transfusion Threshold} = \text{Phototherapy Threshold} + 5\text{ mg/dL}$$

$$\text{% of Phototherapy Threshold} = \left( \frac{\text{Serum Bilirubin}}{\text{Phototherapy Threshold}} \right) \times 100$$

Worked Example

Consider an infant evaluated at 48 hours post-birth with a blood test result of 12 mg/dL total serum bilirubin:

1. Identify Age Bracket: At 48 hours, the infant enters the 48–71 hour monitoring window.
2. Determine Risk Band:
   • Low Intermediate zone cutoff at 48h starts at $12.0\text{ mg/dL}$.
   • Because $12.0\text{ mg/dL} \ge 12.0\text{ mg/dL}$, the risk band is Low Intermediate.
3. Evaluate Phototherapy Proximity:
   • Phototherapy threshold at 48h = $18\text{ mg/dL}$.
   • Margin below threshold = $18 - 12 = 6.0\text{ mg/dL}$.
   • Percentage of threshold = $(12 / 18) \times 100 = 66.7%$.
4. Evaluate Exchange Transfusion Margin:
   • Exchange threshold = $18 + 5 = 23\text{ mg/dL}$.
   • Margin of safety = $23 - 12 = 11.0\text{ mg/dL}$.
5. Clinical Urgency:
   • A Low Intermediate designation warrants Routine follow-up evaluation within 24 hours.

Clinical Context & Safety

Hyperbilirubinemia management aims to prevent acute bilirubin encephalopathy and kernicterus, a rare but severe neurological condition caused by unmanaged bilirubin crossing the blood-brain barrier.

Transcutaneous bilirubin (TcB) devices offer rapid non-invasive screening, but serum blood tests (TSB) remain the gold standard for treatment decisions.

Infants with hemolysis (ABO or Rh incompatibility), G6PD deficiency, asphyxia, lethargy, or prematurity (<38 weeks) are at increased risk for bilirubin neurotoxicity and require lower treatment thresholds according to American Academy of Pediatrics guidelines.

Always consult a board-certified pediatrician or neonatologist for diagnostic and therapeutic plans.