Around 60 % of term and 80 % of preterm newborns develop visible jaundice in the first days of life. In most cases it is benign — but in some infants total serum bilirubin (TSB) rises to a level that needs phototherapy, and rare extreme values can cause permanent brain injury (kernicterus).
The Bhutani nomogram (Bhutani, Johnson & Sivieri, Pediatrics 1999) maps any TSB value to an hour-specific percentile. Four risk zones predict how likely significant hyperbilirubinemia becomes — and whether closer follow-up or treatment is appropriate.
Why a single number tells you very little
A TSB of 10 mg/dL (171 µmol/L) on its own says nothing. Postnatal age in hours is decisive. At 12 hours of life, 10 mg/dL is clearly abnormal — at 5 days of life, it is often normal. The nomogram gives an age-specific reference corridor instead of a single threshold.
That is why the old rule of thumb "treat above 12 mg/dL" is outdated. The much more useful question is: is the value above or below the 95th percentile for the current postnatal age?
The four risk zones
| Percentile | Zone | Recommendation |
|---|---|---|
| < 40th | Low risk | Routine follow-up |
| 40th – 75th | Low intermediate | Re-check in 24 – 48 h |
| 76th – 94th | High intermediate | Close follow-up; review risk factors |
| ≥ 95th | High risk | Prompt medical evaluation |
In Bhutani's original cohort, 40 % of infants in the high-risk zone developed significant hyperbilirubinemia, compared with under 1 % in the low-risk zone. That is why the nomogram is the leading screening tool before discharge from the maternity ward.
Risk factors that lower the threshold
- Hemolysis — ABO/Rh incompatibility, G6PD deficiency, hereditary spherocytosis. Significantly lowers treatment thresholds.
- Lower gestational age — 35–36 weeks: less liver mass, slower bilirubin conjugation.
- Feeding difficulties / weight loss > 8 % — fewer stools, more enterohepatic recycling of bilirubin.
- Cephalohematoma / bruising — extravasated blood is metabolised to additional bilirubin.
- Sibling who needed phototherapy — familial clustering signals genetic predisposition.
- East Asian ancestry — higher incidence, often UGT1A1 variants affecting bilirubin conjugation.
When phototherapy is indicated
The AAP 2022 guideline provides separate threshold tables for each gestational age (35 – 38+ weeks) and risk-factor profile. Simplified: the younger the infant, the lower the gestational age, and the more risk factors present, the earlier treatment is started.
Phototherapy converts bilirubin in the skin into water-soluble isomers that are excreted without hepatic conjugation. It is safe and usually sufficient. Exchange transfusion is reserved for extreme values where kernicterus is imminent.
What parents can spot
- Yellowing in daylight — starts on the face and progresses downward. Yellow legs and feet usually mean a clearly elevated value.
- Sleepy, weak feeding — a warning sign, especially in the first 72 h.
- Pale stools, dark urine — may suggest a cholestatic (conjugated) hyperbilirubinemia, which behaves differently from the typical unconjugated form.
Related topics & calculators
- APGAR score — first-minute and five-minute newborn assessment. Read the APGAR guide.
- Baby feeding amount — adequate intake reduces bilirubin via more frequent stooling. See the feeding-amount guide.
- Baby milestones — what normal development looks like in the first weeks. See the milestone tracker guide.
Estimate your newborn's bilirubin risk
Bhutani nomogram, anonymous, instant. Converts mg/dL ⇄ µmol/L automatically.
Open the bilirubin calculator →Frequently asked questions
At what value does my baby need phototherapy?
There is no single number. AAP 2022 thresholds depend on postnatal age, gestational age, and risk factors. For a healthy term newborn, typical day-3 thresholds sit between 18 and 21 mg/dL — much lower with risk factors. The pediatrician makes the decision.
Does sunlight help?
No. Direct sun exposure risks sunburn and overheating. Effective phototherapy uses defined wavelengths (440–470 nm) at controlled intensity — delivered in hospital or with explicitly prescribed home devices.
How often should bilirubin be measured?
At least once before discharge from the maternity ward, ideally with a transcutaneous bilirubinometer or serum sample. Early-discharge infants and those with risk factors need closer surveillance until values clearly plateau.
What is kernicterus?
Kernicterus is the most severe form of bilirubin toxicity: unconjugated bilirubin crosses the blood–brain barrier and damages the basal ganglia. It is now extremely rare because Bhutani-based screening and AAP thresholds usually catch high-risk infants in time.