Trancutaneous Bilirubin as Predictor of Phototherapy
I read with interest the article by Papacostas et al1 describing the role of sixth-hour transcutaneous bilirubin (TcB) in identifying infants at low and high risk of phototherapy (PTX) in the first 24 hours. They reported a cutoff value on 3.0 to 5.3 mg/dL as the lower and higher risk for PTX for a subset of infants with ABO incompatibility and positive direct antiglobulin test. Using the likelihood ratio nomogram, as described by Jaeschke et al,2 the posttest probability for the lower risk TcB of 3 mg/dL would be 37% (the pretest probability 15%, likelihood ratio was 3.7), whereas the posttest probability for the upper-risk TcB of 5.3 mg/dL would be 97% (the pretest probability 70%; likelihood ratio was 20.9). The higher probability noted with higher bilirubin level was expected. In fact, a bilirubin of 5 mg/dL at 6 hours of life, for infants with ABO incompatibility, is already an indication for PTX as per the management guidelines published by the American Academy of Pediatrics (AAP).3
The data evaluated by Papacostas et al1 were 5 years old. The phototherapy was required in 281 of 772 (36.4%); 156 (20.2%) in the first 24 hours. It would be interesting to know how many infants out of 156 were started on PTX at 6 hours of life. If their practice guideline has not changed, a comparative data from recent years would be very informative to see the change in PTX percentages in the first 24 hours.
In clinical practice, once the bilirubin level reached the threshold for PTX on the hourly-based AAP nomogram,3 the infant would be started on the PTX irrespective of the projected risk for PTX at 24 hours. The prediction model would be of value in justifying hospital stay and counseling the parents in cases of early discharge.
In conclusion, TcB measurement at 6 hours of life in cases of ABO incompatibility with direct antiglobulin test (DAT)-positive status has a screening and predictive role. The decision about starting PTX should be based on the AAP guidelines.
POTENTIAL CONFLICT OF INTEREST: None declared