Biochemistry
Neonatal bilirubin
Neonatal bilirubin measures the yellow pigment produced when red blood cells break down and accumulate in a newborn's blood and skin, the cause of neonatal jaundice. Point-of-care testing allows rapid screening and monitoring at the cot side, so babies who may need phototherapy or further investigation are identified quickly.
Why it is measured
Most newborns develop some jaundice, but very high bilirubin can cross into the brain and cause kernicterus, so timely measurement guides safe, evidence-based treatment. Rapid bedside results shorten delays and reduce the number of heel-prick blood samples a baby needs.
| Typical range | Neonatal total bilirubin is interpreted against age-in-hours and gestation-specific treatment-threshold charts (for example NICE or the Bhutani nomogram), not a single fixed reference interval. Cord or birth blood is typically below about 35 micromol/L (about 2 mg/dL). Physiological jaundice commonly peaks around days 3 to 5; in healthy term babies, phototherapy is often considered above roughly 250 to 350 micromol/L (about 15 to 20 mg/dL) depending on exact age in hours and risk factors. Values vary by method (transcutaneous screening versus whole-blood or serum) and should be confirmed with a laboratory or blood-based total serum bilirubin when near a treatment threshold. Conversion: 1 mg/dL is approximately 17.1 micromol/L. |
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| Sample | Two approaches are used at the point of care. Transcutaneous meters take a non-invasive reading by shining light onto the skin, usually over the forehead or sternum, with no blood sample needed. Blood-based analysers use a small volume of capillary whole blood, typically from a heel-prick. Transcutaneous screening results at or above the local threshold are confirmed with a blood total serum bilirubin. |
| Turnaround | Seconds. Transcutaneous bilirubinometers give an instant reading, and whole-blood analysers report in well under a minute (around 35 seconds on the Radiometer ABL90 FLEX PLUS). |
Point of care devices that report it
- Dräger Jaundice Meter JM-105 (non-invasive transcutaneous bilirubinometer, cot-side screening)
- Philips BiliChek (non-invasive multi-wavelength transcutaneous bilirubinometer)
- Radiometer ABL90 FLEX PLUS (whole-blood blood gas analyser reporting a neonatal bilirubin parameter)
- Radiometer ABL800 FLEX (whole-blood blood gas analyser reporting neonatal bilirubin)
Questions, answered
Can a transcutaneous bilirubinometer replace a blood bilirubin test?
Transcutaneous devices are validated screening tools that estimate bilirubin without a blood sample, which reduces the number of heel-pricks a baby needs. Most guidelines treat them as a screen: readings at or above a defined level, or readings in a baby already on phototherapy, are confirmed with a blood-based total serum bilirubin before treatment decisions are made. They are not considered a substitute for a laboratory result close to treatment thresholds.
Does phototherapy affect transcutaneous readings?
Yes. Phototherapy bleaches bilirubin in the skin, so transcutaneous readings become unreliable once phototherapy has started or on skin that has been exposed to the light. Blood-based total serum bilirubin is generally used for monitoring during and after phototherapy. Local protocols vary, so follow your unit's guidance on when transcutaneous screening can resume.
Why are results reported sometimes in micromol/L and sometimes in mg/dL?
UK and most SI-unit laboratories report bilirubin in micromoles per litre (micromol/L), while many US sources use milligrams per decilitre (mg/dL). To convert, multiply a mg/dL value by about 17.1 to get micromol/L. Always check which units a device and threshold chart use, because treatment thresholds are unit-specific.