Neonatal Phototherapy Threshold Calculator
Neonatal Phototherapy Threshold Calculator
Where a measured serum bilirubin sits relative to the NICE CG98 phototherapy line, for a baby born at 38 weeks of gestation or more, by postnatal age in hours. Babies born before 38 weeks have lower thresholds that this page does not carry.
NICE phototherapy line — babies 38 weeks and over
Age in hours + bilirubin → marginA baby born at 39 weeks, now 40 hours old, serum bilirubin 210 µmol/L
The NICE line for babies 38 weeks and over
24 to 96 hours: threshold = 200 + 2.0833 × (hours − 24)
after 96 hours: threshold = 350 µmol/L
headline = measured bilirubin − threshold
- 100 µmol/L at birth
- the NICE phototherapy threshold at 0 hours for a baby of 38 weeks or more. It is the same as the exchange transfusion threshold at 0 hours, which is why any jaundice in the first hours of life is treated as an emergency
- the two slopes
- the line climbs 100 µmol/L over the first 24 hours and a further 150 µmol/L over the next 72. Both segments are exactly linear through every point NICE tabulates, so reading this calculator and reading the graph give the same answer
- 350 µmol/L plateau
- reached at 96 hours and flat thereafter. NICE’s published table stops at ’96+ hours’ for that reason
- the margin
- measured bilirubin minus threshold. Negative means below the line, positive means at or above it. The margin rather than the threshold is the headline because a calculator can print only one number, and this is the one the reader is trying to work out
- 212, 237, 262, 287
- the whole numbers NICE prints at 30, 42, 54 and 66 hours. They are 212.5, 237.5, 262.5 and 287.5 truncated for the printed table — this calculator uses the line rather than the truncation, so it can differ from the table by half a micromole
- what the line ignores
- gestation below 38 weeks, which lowers it; and every clinical modifier — haemolysis, sepsis, the rate of rise, albumin, acidosis and clinical signs of bilirubin encephalopathy — none of which move the printed threshold but all of which move the decision
Worked example
A baby born at 39 weeks, now 40 hours old, serum bilirubin 210 µmol/L
40 hours is past 24, so the threshold is on the second segment: 200 + 2.0833 × (40 − 24) = 200 + 33.3 = 233.3 µmol/L
Margin = 210 − 233.3 = −23 µmol/L, so the baby is 23 µmol/L below the phototherapy line
That is inside 50 µmol/L of the threshold, which is where NICE's own table advises repeating the measurement in 6 to 12 hours
Six hours later the threshold will have risen to 200 + 2.0833 × 22 = 245.8 µmol/L. If the bilirubin has not moved, the margin widens to −36. If it has risen by 30 µmol/L, the baby is above the line
The same 210 µmol/L at 18 hours of age would be compared with 100 + 4.1667 × 18 = 175 µmol/L, a margin of +35 — comfortably above the line and requiring phototherapy
The same 210 µmol/L at 20 hours in a baby born at 34 weeks cannot be read here at all: the NICE chart for 34 weeks carries a lower line, and this page does not hold it
The NICE phototherapy line, babies 38 weeks and over
| Postnatal age (hours) | Phototherapy threshold (µmol/L) | Exchange transfusion threshold (µmol/L) |
|---|---|---|
| 0 | 100 | 100 |
| 6 | 125 | 150 |
| 12 | 150 | 200 |
| 18 | 175 | 250 |
| 24 | 200 | 300 |
| 30 | 212 | 350 |
| 36 | 225 | 400 |
| 42 | 237 | 450 |
| 48 | 250 | 450 |
| 60 | 275 | 450 |
| 72 | 300 | 450 |
| 84 | 325 | 450 |
| 96 and beyond | 350 | 450 |
What this page does and does not cover
| Situation | Covered here? |
|---|---|
| Baby born at 38 weeks or more | Yes — the NICE line above |
| Baby born before 38 weeks | No. Use the NICE treatment threshold graph for that week of gestation |
| Deciding whether to start phototherapy | No. That is a clinical decision made against local policy, the trajectory and the whole clinical picture |
| Comparing NICE with the 2022 AAP thresholds | No. They are different guidelines with different numbers; use whichever your unit works to, and only that one |
| Jaundice in the first 24 hours | Urgent assessment regardless of the number — see the note under every result |
| Prolonged jaundice beyond 14 days (21 in a preterm baby) | No. That needs a split bilirubin, not a threshold |
A line on a graph, and everything the line does not know
Unconjugated bilirubin is neurotoxic. Free bilirubin crossing into the brain of a newborn causes acute bilirubin encephalopathy and, if it persists, the permanent movement disorder and hearing loss of kernicterus. Phototherapy converts bilirubin in the skin into water-soluble isomers that can be excreted without conjugation, and it works: the reason kernicterus is now rare in the United Kingdom is that jaundiced babies are measured and treated against a threshold rather than assessed by eye.
The threshold is not a fixed number. It rises with postnatal age, because physiological jaundice peaks and falls on a predictable course, so the same bilirubin means something quite different at 12 hours and at four days. It also falls with prematurity, because a preterm baby has less albumin, a less mature blood-brain barrier and a greater risk of bilirubin injury at any given level. That is why NICE publishes a separate graph for every week of gestation rather than one table, and why this page — which holds only the line for babies born at 38 weeks or more — is silent about preterm babies rather than offering an approximation of their thresholds.
Reading a value off the line is the easy part. What the line cannot see is most of what matters. It does not know whether the jaundice is haemolytic, and a positive direct antiglobulin test, a rising reticulocyte count or a bilirubin climbing faster than about 8.5 micromoles per litre per hour all change the urgency without changing the printed number. It does not know the serum albumin, which determines how much bilirubin is bound and therefore harmless. It does not know whether the baby is septic, acidotic, dehydrated or feeding poorly, all of which shift the risk. And it cannot see the baby: lethargy, a high-pitched cry, hypertonia, opisthotonos or poor feeding in a jaundiced newborn are signs of acute bilirubin encephalopathy and are an emergency at any bilirubin level.
Two further cautions belong on any page that prints a jaundice threshold. The first is that guidelines disagree. The 2022 revision of the American Academy of Pediatrics guideline raised its phototherapy thresholds and stratified them by neurotoxicity risk factors, and it does not give the same answer as NICE for the same baby. A unit works to one guideline, consistently, and mixing them produces decisions that follow neither. The second is timing: jaundice visible in the first 24 hours of life is never physiological. It needs a serum bilirubin within two hours and urgent medical review, whatever the level turns out to be, because the causes that produce it — haemolytic disease, congenital infection, sepsis — are the causes that do harm quickly.
Frequently asked questions
At what bilirubin level does a newborn need phototherapy?
There is no single level. Under NICE CG98, a baby born at 38 weeks or more needs phototherapy above 100 µmol/L at birth, 200 µmol/L at 24 hours, 300 µmol/L at 72 hours and 350 µmol/L from 96 hours onwards. Babies born before 38 weeks have lower thresholds set out on a separate NICE graph for each week of gestation.
Why does this calculator not cover preterm babies?
Because the NICE thresholds for gestations below 38 weeks are published as per-week graphs whose values could not be verified from a retrievable primary source, and an approximated threshold on a page like this would be worse than no threshold at all. Plot a preterm baby on the NICE chart for that week of gestation instead.
Do NICE and the AAP give the same phototherapy thresholds?
No. The 2022 AAP revision uses higher thresholds than it previously did and stratifies them by gestational age and neurotoxicity risk factors, so it and NICE can disagree by a wide margin for the same baby. Work to whichever guideline your unit has adopted, and to that one only.
What should be done about jaundice in the first 24 hours of life?
Treat it as urgent whatever the level. Measure the serum bilirubin within 2 hours, repeat it every 6 hours until it is below the treatment threshold and falling, and arrange urgent medical review to look for haemolysis, sepsis or congenital infection. Jaundice this early is never physiological.
Can a transcutaneous bilirubin reading be used with these thresholds?
Only as a screening tool. NICE restricts transcutaneous bilirubinometry to babies of 35 weeks or more who are over 24 hours old, and requires any reading above 250 µmol/L to be confirmed on a serum sample. Treatment decisions are made on serum bilirubin.
Related calculators
References
- National Institute for Health and Care Excellence. Jaundice in Newborn Babies Under 28 Days. NICE clinical guideline CG98. London: NICE; 2010, updated 2023 — treatment threshold table and treatment threshold graphs.
- Kemper AR, Newman TB, Slaughter JL, et al. Clinical practice guideline revision: management of hyperbilirubinemia in the newborn infant 35 or more weeks of gestation. Pediatrics. 2022;150(3):e2022058859.
- American Academy of Pediatrics Subcommittee on Hyperbilirubinemia. Management of hyperbilirubinemia in the newborn infant 35 or more weeks of gestation. Pediatrics. 2004;114(1):297–316.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.