Early formation of bilirubin isomers during phototherapy for neonatal jaundice: effects of single vs. double fluorescent lamps vs. photodiodes.

BACKGROUND

In neonatal jaundice, phototherapy converts bilirubin to more polar photoisomers which can be excreted without conjugation. We measured changes in the concentration of bilirubin Z,E-photoisomer during the first 4 h of intensive phototherapy using single fluorescent lights as a reference, compared to double fluorescent lights, and a single unit of photodiodes.

METHODS

Neonates (N = 42; birth weight: 1,200-4,690 g; gestational age: 28-42 wk) were studied during phototherapy. Infants were randomized to: (i) single, or (ii) double fluorescent phototherapy; or (iii) single unit photodiodes. Irradiance was measured. Serum bilirubin (by cooximetry) and Z,E bilirubin (by high-pressure liquid chromatography) were measured at 0,15, 30, 60, 120, and 240 min after the start of phototherapy. Data were analyzed with a linear mixed model.

RESULTS

There was a highly significant increase of Z,E-bilirubin over time (P < 0.0001), starting at 15 min. Photoisomers reached ~25% of total bilirubin concentration after 4 h. However, there were no significant differences between the three randomized groups in spite of significantly higher irradiance using double fluorescent lights vs. single fluorescent or photodiodes.

CONCLUSION

Formation of bilirubin photoisomers is rapid, and occurs early during intensive phototherapy for neonatal jaundice. The rate and level of photoisomerization was not influenced by irradiance and light source.