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Original Investigation | Journal Club

Association Between Laboratory Calibration of a Serum Bilirubin Assay, Neonatal Bilirubin Levels, and Phototherapy Use

Michael W. Kuzniewicz, MD, MPH1,2,3; Dina N. Greene, PhD4; Eileen M. Walsh, RN, MPH1; Charles E. McCulloch, PhD5; Thomas B. Newman, MD, MPH1,3,5
[+] Author Affiliations
1Division of Research, Kaiser Permanente Northern California, Oakland
2Division of Neonatology, Kaiser Permanente Northern California, Oakland, California
3Department of Pediatrics, University of California, San Francisco
4Department of Laboratory Medicine, University of Washington, Seattle
5Department of Epidemiology and Biostatistics, University of California, San Francisco
JAMA Pediatr. 2016;170(6):557-561. doi:10.1001/jamapediatrics.2015.4944.
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Importance  The American Academy of Pediatrics treatment recommendations for neonatal jaundice are based on age-specific total serum bilirubin (TSB) levels. In May 2012, Ortho Clinical Diagnostics adjusted the calibrator values for Vitros Chemistry Products BuBc Slides (Ortho Clinical Diagnostics), a widely used method to quantify TSB, after concerns of positively biased results.

Objective  To investigate the association between recalibration of a reflectance spectrophotometry serum bilirubin assay and TSB levels and phototherapy use among newborns.

Design, Setting, and Participants  Descriptive study comparing TSB levels and phototherapy use before and after recalibration at Kaiser Permanente Northern California, a large, integrated health care delivery system. The study evaluated live births at or after 35 weeks’ gestation at 12 facilities that used universal serum bilirubin screening before (January 1, 2010, through April 30, 2012; n = 61 677) and after (July 1, 2012, through December 31, 2013; n = 42 571) recalibration. The analysis took place in December 2015.

Intervention  Recalibration of bilirubin testing instruments.

Main Outcomes and Measures  Proportions of newborns with (1) at least 1 TSB value at or above 15 mg/dL; (2) at least 1 TSB level exceeding the American Academy of Pediatrics phototherapy threshold; (3) phototherapy during the birth hospitalization; and (4) at least 1 readmission for phototherapy.

Results  In 104 420 infants (61 677 in the prerecalibration period and 42 511 in the postrecalibration period), a TSB was obtained in 99.2% of infants during birth and in 99.5% of infants within the first 30 days after birth. The postrecalibration period was associated with a 1.25 mg/dL (95% CI, 1.19-1.31; P < .001) decrease in mean maximum TSB, which led to a 39% relative reduction (from 20.4% to 12.4%) in infants with a TSB level of 15 mg/dL or more and a 51% relative reduction (from 9.3% to 4.5%) in infants with a TSB level that was at or above the American Academy of Pediatrics phototherapy threshold. Phototherapy during birth hospitalizations was reduced by 59% (absolute risk reduction, 5.5%; 95% CI, 4.7%-6.1%) and readmissions for phototherapy by 53% (absolute risk reduction, 1.8%; 95% CI, 1.4%-2.3%).

Conclusions and Relevance  Modest recalibration-induced reductions in mean TSB concentrations was associated with a significant reduction in the percentage of infants with clinically significant hyperbilirubinemia. Current laboratory accuracy standards are insufficient to detect biases that can have significant clinical effect. These data underline the need for increased integration of laboratory expertise into clinical guidelines and to support international initiatives to standardize laboratory measurements.

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Figure.
Monthly Rates of Phototherapy Administration and Hyperbilirubinemia

In June 2012, monthly rates of phototherapy administration during the birth hospitalization and readmissions for phototherapy dropped precipitously along with the percentage of infants with hyperbilirubinemia. To convert bilirubin to micromoles per liter, multiply by 17.104.

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A Huge Sample Size May Be “Too Much Of a Good Thing”
Posted on April 17, 2016
Sameer Al-Abdi
Department of Pediatrics, King Abdulaziz Hospital in Al-Ahsa, MNGH, Saudi Arabia
Conflict of Interest: None Declared
I have read this article with great interest. However, five issues need to be contemplated when interpreting the results.

1. The sample size was huge which rendered negligible differences to be statistically significant.1 This was very clear in table 1 as very negligible differences between five variables were statistically significant.

2. Relative risk reduction (RRR) is more impressive than absolute risk reduction (ARR) in particular when rate of event is low in the control group.2 In postrecalibration period, readmission for phototherapy was reduced by 53% (RRR) while ARR was 1.8% only (number need to treat: 55; 95% CI: 43-71).

3. The advantage of reduction in readmissions for phototherapy may be offset by the increased length of stay for birth hospitalization in postrecalibration period (2.5 days vs 2.2 days).

4. Though the results are logic, it is difficult to point to one factor as the main cause for the results in a comparative-historical analysis without controlling for other potential confounders including other changes in practice.

5. Despite that the study outcomes are important, more importantly to know whether these advantages were offset by increased rates of TSB within exchange transfusion zone or kernicterus.

References
1. Sullivan GM, Feinn R. Using Effect Size—or Why the P Value Is Not Enough. Journal of Graduate Medical Education. 2012;4(3):279-282.

2. Barratt A, Wyer PC, Hatala R, et al. Tips for learners of evidence-based medicine: 1. Relative risk reduction, absolute risk reduction and number needed to treat. CMAJ : Canadian Medical Association Journal. 2004;171(4):353-358.

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