Accuracy of bilirubin on the Siemens RAPIDPoint 500 blood gas analyser: A data mining study

Blood gas analysers which can measure bilirubin in whole blood are commonly available in neonatal intensive care units; however, the accuracy of these measurements is not well established. We sought to determine accuracy of whole blood bilirubin on the Siemens RAPIDPoint 500 blood gas analyser with reference to formal laboratory total serum bilirubin on the Ortho Vitros 5600.

A method comparison of the bilirubin results from the blood gas analysers compared with the chemistry analysers was performed by data mining of results obtained as part of routine patient care. Results were included if patients underwent bilirubin testing by blood gas analyser and formal TSB, with both samples being collected within 20 min. Retrospective laboratory data was collected over a 28-month period, 1 January 2019 to 1 May 2021.

449 eligible sample pairs were included. A Bland-Altman plot was generated to identify systematic differences between the methods. A mean bias of -11 μmol/L was observed with 95% limits from -60 μmol/L to 38 μmol/L. Some blood gas bilirubin results were up to 70 μmol/L lower than formal TSB measurements around the clinically significant concentration range of 200 to 300 μmol/L.

Clinicians need to be aware of potential differences between the results from their blood gas analysers compared to formal TSB results. Sole reliance on blood gas bilirubin results which underestimate TSB may lead to under-recognition of neonatal jaundice that meets treatment thresholds. Formal measurement of TSB should be sought to inform decisions regarding treatment of neonatal jaundice.