Transcutaneous Bilirubinometers to Guide Treatment of Hyperbilirubinaemia in Neonates

The estimation of hyperbilirubinaemia in the neonatal population is a critical step in the management of jaundice. Historically, the ordering of a laboratory total serum bilirubin (TSB) would have been prompted by the suspicion of, or visual detection of jaundice. Where bilirubin levels are rising rapidly it is essential to measure bilirubin levels as soon as possible (within 6 hours) in babies with suspected jaundice so that the appropriate treatment can be started. This is achievable for inpatient cases but can prove difficult in the outpatient population.

A transcutaneous bilirubinometer, in the hands of a trained healthcare professional, can be used to assess patient transcutaneous bilirubin (TCB) levels to indicate if treatment is required. Decisions on whether to transfer the baby to hospital, or to monitor progress in the community through the relevant midwifery services, could be made if these devices were widely available.

Official Guidance

Guidance on the steps healthcare professionals must take in the management of jaundice in newborn babies under 28 days old can be found in the NICE guideline here https://www.nice.org.uk/guidance/cg98

Guidance on the measurement of bilirubin levels in babies more than 24 hours old is covered here in the NICE Quality Standard QS57. According to this standard ‘Transcutaneous bilirubinometers, although not as accurate as measuring serum bilirubin, are more accurate than visual inspection alone, are non-invasive, can be used in the community and provide instant results.’

The use of phototherapy as a treatment for hyperbilirubinaemia reduces the need for exchange transfusion which is normally restricted for use in only the most severe cases. Kernicterus is a rare but serious consequence of untreated jaundice in neonates where excessive levels of bilirubin in the blood can cause brain or central nervous system damage. Bilirubin is able to cross the blood-brain barrier. More information on the condition can be found here https://www.nhs.uk/conditions/jaundice-newborn/complications/

Babies may be at risk of developing kernicterus if:

•             they have a very high level of bilirubin in their blood

•             the level of bilirubin in their blood is rising rapidly

•             they don’t receive any treatment

Rapidly detecting a dangerous rise in blood bilirubin concentration is essential in order to optimise treatment and avoid negative patient outcomes.

When to use a Transcutaneous Bilirubinometer

Following discharge, babies can develop jaundice so it is imperative that parents can access a service that allows for the measurement of bilirubin in their homes or a community healthcare setting. In the community it is difficult to obtain a serum bilirubin measurement, with a quick enough turnaround time, to allow for the most accurate assessment of the extent of jaundice.

In this scenario, and in the absence of a postnatal service equipped with rapid diagnostic tools such as a transcutaneous bilirubinometer, the baby is likely to be taken into hospital for further investigations. This can be very disruptive, cause distress for the parents and the baby, and put additional pressure on healthcare resources. A transcutaneous measurement of bilirubin, performed accurately by a trained healthcare professional, can give sufficient clinical information which could avoid a hospital visit. Results are instantly obtained which can be checked against a number of standardised criteria which indicates the next steps.

Guidance for Use (from QS57)

When measuring the bilirubin level in babies more than 24 hours old:

• use a transcutaneous bilirubinometer in babies with a gestational age of 35 weeks or more (always use serum bilirubin measurement to determine the bilirubin level in babies less than 35 weeks’ gestational age)
• if a transcutaneous bilirubinometer is not available, measure the serum bilirubin
• if a transcutaneous bilirubinometer measurement indicates a bilirubin level greater than 250 µmol/litre check the result by measuring the serum bilirubin
• always use serum bilirubin measurement for babies at or above the relevant treatment thresholds for their postnatal age, and for all subsequent measurements

Verification of Performance

Obtaining accurate transcutaneous bilirubin results using these devices is subject to user variation, sampling site (forehead, sternum) and whether duplicate measurements are taken. Services adopting bilirubinometers must involve the medical laboratory where comparisons with total serum bilirubin (TSB) must be made before adopting the device for clinical use.

Important factors to establish are imprecision and bias. If the bias is constant then paediatric clinicians will be able to establish a safe cut off in relation to bilirubin concentrations that indicate the need for treatment. For instance, if the true bilirubin concentration is 250 µmol/litre and the bilirubinometer has been shown to have a constant bias at this concentration of 30 µmol/litre, the paediatric team would need to amend their protocol for treatment to take the bias into account.

In this example a bilirubinometer reading of 250 µmol/litre could actually be 280 or 220 µmol/litre depending on whether the bias is negative or positive. Underestimation of the bilirubin could result in missed interventions. The use of a bilirubinometer should lead to a reduction in unnecessary interventions rather than an increase, so setting the threshold accordingly is imperative.

The following study, https://pubmed.ncbi.nlm.nih.gov/29601801/ showed that almost 40% of total serum bilirubin (TSB) measurements in the outpatient newborn population could be avoided using a transcutaneous bilirubin cut off of 222 µmol/litre. ‘The use of a transcutaneous bilirubinometer could reduce the number of invasive blood sampling [events] for the determination of serum bilirubin.’ NB. This value will be device specific.

Skin pigmentation can impact on the accuracy of clinical decisions with the following study of indigenous Zimbabwean babies https://mhnpjournal.biomedcentral.com/articles/10.1186/s40748-017-0070-0 stating the following, ‘Melanin affects the clinical estimation of jaundice in the newborn. Clinical assessment of jaundice often leads to over or underestimation of jaundice and results in unnecessary blood draws from the baby with resultant maternal anxiety.’ Verification of the performance of transcutaneous bilirubinometers is essential in different ethnic populations to understand any under or overestimation of TCB. This study https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4306797/ found discrepancies between measurements taken from African-American newborns and varied across different vendor devices, further emphasising the need for service specific verification of device performance.

Conclusion Many published studies have drawn the following conclusion. TCB measurement can be safely used as a screening tool for assessment of neonatal jaundice, and invasive painful procedures for bilirubin estimation could be avoided by introducing the use of transcutaneous bilirubinometers. This is particularly important for midwifery teams providing home visits or healthcare professionals providing services in locations such as community diagnostic centres (CDCs).