7 On account of the high costs involved and the requirement of specialized personnel, these instruments are used mainly in laboratories of large hospitals. They usually base the direct determination of bilirubin on diazo (Jendrassik Grof) and vanadate oxidase chemical reactions, or on variants. Routine laboratory bilirubin measurement is commonly performed with multichannel instruments that provide values for conjugated (direct), unconjugated (indirect), and TSB concentrations. 5 For a thorough understanding in the subsequent paragraphs of the so-called science of measurement and of terms such as TSB accuracy, trueness, metrological traceability, and measurement uncertainty, we refer to the definitions and terminology provided by the International Vocabulary of Metrology. 4 This was followed by Jendrassik and Grof who refined and modified the diazo reactions in 1938. 1, 2 Van den Bergh and Snapper described their important diazo reaction in 1913 3 and the colorimetric determination by Malloy and Evelyn was published in 1937. A vast number of methods to determine bilirubin in human serum have been developed since it was first reported in 1858 by Frerichs (Gmelin reaction). Over the past decades, bilirubin measurement for severe neonatal hyperbilirubinemia (SNH) identification has constituted a major challenge. An essential prerequisite for bilirubin measurements is that they are accurate and precise to manage jaundiced newborn infants appropriately. Bilirubin measurements are key to the management of neonatal jaundice. International guidelines for the management of neonates with unconjugated hyperbilirubinemia include treatment thresholds that are based on total serum bilirubin (TSB) concentrations. Impact: Manufacturers should make TSB test results traceable to the internationally endorsed total bilirubin reference measurement system and should ensure permissible limits of measurement uncertainty. We review novel diagnostic point-of-care (POC) bilirubin measurement methods and analytic methods for determining bilirubin levels in biological matrices other than blood. What does this article add to the existing literature? We provide analytic performance data on total serum bilirubin (TSB) as measured during recent EQA surveys. External quality assessment (EQA) plays an important role in revealing inaccuracies in diagnostic bilirubin measurements. Key message: Bilirubin measurements in blood remain the gold standard for diagnosis and treatment of severe neonatal hyperbilirubinemia (SNH). Novel analytic methods may, apart from bilirubin, include the determination of bilirubin photoisomers and bilirubin oxidation products in blood and even in other biological matrices. This implies correct implementation of internationally endorsed reference measurement systems as well as participation in external quality assessment programs. Total serum bilirubin test results should be accurate within permissible limits of measurement uncertainty to be fit for clinical purposes. Novel point-of-care bilirubin measurement methods, such as the BiliSpec and the Bilistick, would benefit many newborn infants, especially in low-income and middle-income countries where the access to costly multi-analyzer in vitro diagnostic instruments is limited. The present paper describes different methods currently available to assess hyperbilirubinemia in newborn infants. Invasive bilirubin measurements remain the gold standard for the diagnosis and treatment of infants with severe neonatal hyperbilirubinemia.
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