Limitations and opportunities of whole blood bilirubin measurements by GEM premier 4000®

Accuracy and Reliability of Whole Blood Bilirubin Measurements Using a Roche Blood Gas Analyzer for Neonatal Hyperbilirubinemia Screening and Risk Stratification

BACKGROUND

Accurate bilirubin measurements are essential for appropriate management of neonatal hyperbilirubinemia. This study aimed to evaluate the accuracy and reliability of whole blood bilirubin measurements obtained using a Roche blood gas analyzer (Roche TBiL), with total serum bilirubin (TSB) measurements determined by the Ortho VITROS 4600 chemistry system (Ortho TSB) serving as a reference.

MATERIALS AND METHODS

Medical records of hospitalized neonates that underwent simultaneous Roche TBiL and Ortho TSB measurements were reviewed for eligibility selection and data collection. The correlations and differences between two sets of results were determined using Passing-Bablok regression analysis and a Bland-Altman plot, respectively. For eligible newborns, the risk of developing severe hyperbilirubinemia was assessed using the Bhutani nomogram. Weighted kappa analysis was used to evaluate the agreement between risk prediction by the two methods.

RESULTS

We obtained 618 paired Roche TBiL and Ortho TSB results from 309 neonates. Roche TBiL and Ortho TSB measurements showed a good correlation (r = 0.923; 95% CI: 0.905-0.938). Passing-Bablok regression analysis yielded the following equation: Roche TBiL = 0.794 × Ortho TSB + 1.255 mg/dL, with a slope of 0.794 (95% CI: 0.763-0.825) and intercept of 1.255 (95% CI: 1.042-1.417). The average difference between the two methods was 0.1 ± 1.448 mg/dL. A total of 207 neonates were eligible for evaluation of the agreement between the risk-grading methods. Although kappa analysis showed good agreement between the methods, with a weighted kappa of 0.681 (95% CI: 0.610-0.751) across all populations, the values for approximately half of the neonates at intermediate and high risk of hyperbilirubinemia (33/72) were underestimated by Roche TBiL.

CONCLUSION

Our results indicate that Roche TBiL and Ortho TSB measurements in the neonatal population are not consistent. As a point-of-care and trace blood assay, Roche blood gas bilirubin measurements can facilitate primary screening of neonatal hyperbilirubinemia, but it seems to lack accuracy regarding risk stratification, particularly for high-risk newborn individuals.

Analytical performance validation and clinical application of blood gas analyzer on the detection of neonatal bilirubin

BACKGROUND

It is not yet clear whether the trace blood gas analyzer can be used for biochemical detection of newborns. This study aimed to evaluate the reliability of the method for the detection of bilirubin in infants.

METHODS

Based on the Clinical and Laboratory Standards Institute (CLSI) EP15-A2 document, the analytical performance of the blood gas analyzer method for bilirubin detection in neonates was validated. The resulting data of 363 simultaneous bilirubin detection with blood gas analyzer (optical method) and biochemical analyzer (enzymatic method) were reviewed. According to the CLSI EP9-A3 document, the relevance and consistency of the measurement results were evaluated by Pearson correlation analysis, Passing-Bablok regression, and Bland-Altman deviation analysis.

RESULTS

The precision and accuracy of the Werfen GEM 4000 blood gas analyzer for the detection of different levels of bilirubin samples adhered to the manufacturer's statement and industry quality standards. The bilirubin detection values of the 2 methods showed a good correlation, and both of them were significantly correlated (P<0.001). Passing-Bablok regression results showed that the regression equation of the bilirubin detection value of the 2 methods is y = -21.00 + 1.17x, with the slope as 1.17 [95% confidence interval (CI): 1.15 to 1.19], and the intercept was -21.00 (95% CI: -23.62 to -18.71), the data of the 2 sets were not consistent in each concentration range. The Bland-Altman plot demonstrated that the bilirubin detection value of 16/363 cases (4.4%) for the 2 methods exceeded the 95% limits of agreement (95% LoA); of which the maximum bias was -30.34 (95% CI: -38.48 to -22.26) and there were 5/76 cases (6.6%) outside the 95% LoA in the >300 μmol/L group.

CONCLUSIONS

The method for detecting neonatal total bilirubin by trace blood gas analyzer basically meets the clinical requirements and can be used for the preliminary screening of neonatal jaundice. However, for severe hyperbilirubinemia that requires close monitoring of dynamics, a precise enzymatic quantification is required.

Diagnostic methods for neonatal hyperbilirubinemia: benefits, limitations, requirements, and novel developments

Invasive bilirubin measurements remain the gold standard for the diagnosis and treatment of infants with severe neonatal hyperbilirubinemia. The present paper describes different methods currently available to assess hyperbilirubinemia in newborn infants. 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. Total serum bilirubin test results should be accurate within permissible limits of measurement uncertainty to be fit for clinical purposes. This implies correct implementation of internationally endorsed reference measurement systems as well as participation in external quality assessment programs. 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. IMPACT: Key message: Bilirubin measurements in blood remain the gold standard for diagnosis and treatment of severe neonatal hyperbilirubinemia (SNH). External quality assessment (EQA) plays an important role in revealing inaccuracies in diagnostic bilirubin measurements. 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. We review novel diagnostic point-of-care (POC) bilirubin measurement methods and analytic methods for determining bilirubin levels in biological matrices other than blood. 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.

Neonatal hemoglobin affects the accuracy of whole blood bilirubin measurement on GEM Premier 4000 blood gas analyzers

Objectives

Whole blood bilirubin measured on blood gas analyzers is accepted by physicians in neonatal hyperbilirubinemia management since it requires a small sample volume. The accuracy of bilirubin measurement on blood gas analyzers is instrument dependent and remains controversial.

Design and Methods

Bilirubin in adult and umbilical cord whole blood samples, spiked with an unconjugated bilirubin standard, and non-spiked adult plasma samples was measured on a blood gas analyzer (GEM 4000) and a Core Laboratory Chemistry analyzer (Architect c16000) respectively. We also investigated the linear regression for neonatal and adult hemoglobin measured on the blood gas analyzer and the Core Laboratory hematology analyzer (Alinity h-Series).

Results

Plasma bilirubin measured on the blood gas analyzer and the chemistry analyzer was statistically identical. Adult whole blood bilirubin showed slightly increased proportional bias. When umbilical cord whole blood samples were used, the Deming regression showed GEM bilirubin =1.233(Architect) (95% CI 1.199 ~ 1.266)-44.43 ​μmol/L (95% CI -53.6 ​~ ​−35.2). The regression was significantly different from that in plasma (p ​< ​0.001) or adult whole blood (p ​< ​0.001) samples. 36.1% neonatal samples with bilirubin levels >50 ​μmol/L showed that the bias% was above laboratory standards. In addition, the regression of neonatal hemoglobin measurement between the GEM and the Alinity was significantly different from adult hemoglobin (p ​< ​0.01).

Conclusions

Neonatal whole blood bilirubin measurement on blood gas analyzers may be affected by neonatal hemoglobin. The method should be validated using neonatal whole blood samples or samples with a similar matrix before the analyzers are implemented into neonatal hyperbilirubinemia management.

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The bias of neonatal bilirubin measurements between the blood gas analyzer and the chemistry analyzer was investigated.

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Bilirubin in adult plasma and whole blood samples measured on the blood gas analyzer was comparable with the diazo assay.

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Bilirubin in umbilical cord whole blood samples measured on blood gas analyzer was not comparable with the diazo assay.

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In addition, the measurement of neonatal hemoglobin on the blood gas analyzer was not as accurate as adult hemoglobin.