Transcutaneous bilirubin may suffice for neonate jaundice test

Last Updated: 2015-01-21

By Will Boggs MD

NEW YORK (Reuters Health) - Although transcutaneous bilirubin (TcB) levels are generally higher than total serum bilirubin (TSB) levels, the discrepancies are rarely clinically meaningful, researchers say.

"I think that the results suggest that TcB is a reasonable way to screen babies for jaundice in the nursery, with TSB reserved for those whose TcB is above some cut-off value," Dr. James A. Taylor, of the University of Washington, Seattle, told Reuters Health by email.

In previous studies, TcB measurements have shown correlation coefficients with TSB levels ranging from 0.77 to 0.97, but most such studies tended to optimize the accuracy of the measurement. Whether these results are applicable to routine clinical settings is unclear.

Dr. Taylor and colleagues in the Better Outcomes through Research for Newborns (BORN) Network conducted a robust assessment of the accuracy of TcB measurements performed as part of routine clinical care through a retrospective study of 8319 TcB measurements in 4994 newborns, with 925 linked TcB and TSB measurements.

On average, TcB measurements were 0.84 mg/dL higher than their paired TSB measurements (range, 6.9 mg/dL lower to 8.8 mg/dL higher), with an overall correlation between paired measurements of 0.78.

At TSB levels below 5 mg/dL, TcB measurements were generally higher, but when TSB levels were 15 mg/dL or higher, TcB measurements averaged lower than TSB.

TcB values differed from TSB values by 2 mg/dL or more in 28.8% of measurements and by 3 mg/dL or more in 12.1% of measurements, according to the January 19 Pediatrics online report.

The difference between TcB and TSB measurements was 0.67 mg/dL higher in African-American infants than in other infants, and differences were lower at nurseries using the JM-103 meter than at those using the Bilichek meter.

Even after adjusting for TSB level, the difference between TcB and TSB increased with each hour of advancing age.

"Overall, our results and the results of other studies suggest that TcB screening might be most effective at an age when most TSB levels would be expected to be <15 mg/dL," the researchers say.

"Our findings may not be generalizable to the use of TcB in outpatient newborns," they add.

"TcB is a reasonably accurate way to assess jaundice in newborns," Dr. Taylor concluded. "However, because there are occasional substantial differences between TcB and TSB measurements, it is helpful that physicians continue to visually assess newborns for jaundice and obtain a TSB even with a relatively low TcB value if the newborn appears significantly more jaundiced than he/she should, based on the TcB."

All this assumes that TSB measurements themselves are accurate, a notion Dr. M. Jeffrey Maisels, of Beaumont Children's Hospital in Royal Oak, Michigan, calls into question in his related editorial. "A 2008 American College of Pathologists Neonatal Bilirubin survey revealed that TSBs measured by several established laboratory methods were 2 to 5 mg/dL higher than the reference method."

"Thus, at least in some cases, what appear to be falsely low TcB levels could be due to erroneously high TSB measurements," he notes.

"False-negative TcBs can be reduced by setting TcB cut points below the TSB levels that might warrant investigation or treatment," Dr. Maisels says. "Thus if we measure the TSB whenever the TcB is 13 or 14 mg/dL or higher, the chance of missing the need for phototherapy in a four-day-old infant is low. Pediatricians in five of our affiliated office-based practices and residents in our hospital-based follow-up clinic have been following our recommended TcB cut points for six years and we have yet to encounter a significant problem with TcBs."

Dr. Manoj Kumar, of the University of Alberta's Neonatal Division in Edmonton, Canada, told Reuters Health by email, "It is a sub-optimal study, as compared to the better conducted prospective studies that exist on this topic, thus of limited clinical utility. Allowing time differences of up to two hours between TcB and TSB estimation during early neonatal period could have significantly impacted the true TcB-TSB differences that would have existed. This is a serious flaw."

"Unfortunately, this study may unnecessarily scare some health workers from using such point-of-care devices in practice," Dr. Kumar said.

Dr. William D. Engle, medical director of the newborn nursery at Parkland Health and Hospital System, University of Texas Southwestern Medical Center at Dallas, told Reuters Health by email, "If an infant has significant risk factors or the level of jaundice seems to suggest a bilirubin level greater than the TcB value, by all means check a TSB. The clinician needs to remember that the TSB, while the current clinical 'gold standard,' may not be perfect either, and inter-lab variability using the same samples has been demonstrated."

"The glass is more than half-full," Dr. Engle said. "The percentage of values in which the TcB underestimated the TSB by at least 3 mg/dL was only 2.2%. So I think the message is that this noninvasive test (preferred by 100% of infants) is quite reliable."

He added, "Vigilance is required whenever some of the clinical situations noted above are present (e.g., significant risk factors) or whenever a TcB value is approaching a level at which an intervention (typically phototherapy) is going to be initiated."

The study was supported by the Academic Pediatric Association, the National Institute of Child Health and Human Development and the National Institutes of Health Office of Research on Women's Health. Dr. Maisels reports having served as a consultant for Draeger Medical; the other authors report no disclosures.

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Pediatrics 2015.