Unbound Bilirubin Levels In Phototherapy-Treated Preterm Infants Receiving Soy-Based Lipid Emulsion

Background Phototherapy is an effective treatment for neonatal jaundice. Treatment indication uses total serum bilirubin (TSB), although unbound bilirubin (Bf) more accurately predicts disability risk. The goals of this investigation were to examine the response of Bf and TSB to phototherapy in preterm infants, and we hypothesized that (i) TSB and Bf respond differently; (ii) the relationship between TSB and Bf is altered; and (iii) unexpected Bf elevations are found.Methods One hundred and seventeen preterm infants <2 kg at birth and receiving (IL) were enrolled; and measurements of TSB and Bf were obtained. TSB was measured by the diazo method and Bf with a fluorescent Bf sensor BL22P1B11-Rh.Results Initial mean (+/- SD) TSB and Bf levels (41.4 +/- 6.9 h) were 8.0 +/- 9.0 mg/dL and 16.9 +/- 12.4 nmol/L (P < 0.05). The rates of rise (ROR) were 0.21 +/- 0.10 mg/dL/h for TSB and 0.38 +/- 0.33 nmol/L/h for Bf. Phototherapy reduced TSB from 8.0 +/- 9.0 to 5.8 +/- 9.4 mg/dL (P = 0.068) but Bf did not change (16.9 +/- 12.4 to 14.1 +/- 9.4 nmol/L P = n.s.). Bf levels were >11 nmol/L in 64, >17 nmol/L in 18, and >22 nmol/L in 7 infants.Conclusions Bf and TSB responded differently. While TSB and Bf correlated well before phototherapy, they did not correlate during phototherapy. TSB showed a trend toward a reduction with treatment, Bf did not. While TSB ROR information is not helpful, ROR Bf data can be utilized to anticipate treatment. Potentially high Bf levels existed before and after phototherapy and the mean Bf level at phototherapy termination remained elevated in a significant proportion of infants.