Transcutaneous Bilirubin Measurement

Transcutaneous bilirubin measurement estimates the serum bilirubin concentration non-invasively. A handheld device shines light on the skin of the forehead or sternum and measures the reflected light, which reflects the bilirubin in the skin.

The value is plotted against an age specific nomogram, which shows the risk of significant hyperbilirubinaemia. It reduces the need for heel prick testing in low risk infants, but it does not replace serum bilirubin when the value is near a treatment threshold.

Usage. It is used in newborn screening for jaundice and in infants with clinical jaundice.

Indications. Routine screening of jaundice before discharge, and follow up of infants with raised bilirubin.

Preparation and technique. The device is placed on clean, unbruised skin, with the infant lying still. Readings are taken at least twice, and the mean is plotted. The infant's age in hours is recorded accurately, since the nomogram depends on age.

Contraindications and precautions. Readings are not valid on bruised skin, after phototherapy, or in sunlight. Skin pigmentation and gestational age affect the relationship between the reading and serum bilirubin.

Interpretation.

• A value well under the nomogram risk line is reassuring, and no further testing is needed in most low risk infants.
• A value near or over the line requires serum bilirubin measurement.
• A value over the treatment line on the nomogram requires immediate serum measurement and clinical review.

Causes of a raised value. Haemolysis, sepsis, breastfeeding failure, G6PD deficiency, and prematurity.

Critical values and findings needing immediate action.

• A transcutaneous value at or over the phototherapy line requires serum confirmation without delay.
• Jaundice with lethargy, poor feeding or signs of kernicterus risk requires urgent assessment.

Limitations and artefacts. The device is less accurate at higher values and in darker skin. Phototherapy, sunlight and bruising lower reliability. Measurement is not a substitute for serum bilirubin when results are close to a threshold.

Follow up tests. Serum total and direct bilirubin, full blood count and reticulocyte count, blood group and direct antiglobulin test, and G6PD assay where haemolysis is suspected.

Special groups. Preterm infants have lower thresholds, and a separate nomogram is used. Infants of mothers with blood group incompatibility need closer monitoring.