Neonatal serum bilirubin from skin reflectance.

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Summary: To provide a noninvasive method for serum bilirubin determination in newborn infants, a reflectometer system was developed using a novel fiber optic arrangement permitting measurement of the light reflected from a small area (3 cm2) of the infant's skin. The reflectometer was operated over the spectral region 400–750 nm with a 30-sec scan time. The reflectometer consisted of a monochomatic light source, fiber optic probe, detector, and data acquisition system Spectral reflectance measurements were performed on the blanched and unblanched skin on the backs of 56 Caucasian newborn infants. Examples of the spectra and corresponding serum bilirubin values of 30 of the infants are presented, illustrating that near 460 nm, the spectral reflectance of the skin decreases with increasing serum bilirubin concentrations. It was also observed that the individualities in epidermal hemoglobin concentration affected the skin reflectance spectra. For this reason the statistical analysis was limited to inclusion of only reflectance spectra of blanched skin. The multispectral analysis of the data was based upon statistical regression analysis investigating the predictability of serum bilirubin level from reflectance spectra. The spectrum between 400 and 740 nm was divided into 5-nm intervals (71 discrete bands). First order linear, multiple linear, and polynomial nonlinear regressions were performed on the spectral reflectance values at each of the intervals with respect to serum bilirubin level. The coefficients of determination (R2 values) are summarized. Because an R2 of only 0.783 was observed at 450 nm, scatter diagrams of serum bilirubin concentration versus spectral skin reflectance at a given wavelength were studied. These indicated that a logarithmic transformation of the data might yield improved results. The double natural logarithm was taken of the 71 discrete spectral reflectance values and a polynomial nonlinear regression was performed with respect to serum bilirubin concentration. The best results of this regression analysis were obtained for a combination of five wavelengths yielding an R2 value of 0.931. The ability to predict serum bilirubin concentration from skin reflectance using this relationship was tested using the original observations. The 95% prediction limit for this empirical relationship was shown to be ± 2 mg/100 ml. Speculation: Spectral reflectance measurements on the newborn skin provide a noninvasive screening method for neonatal jaundice and may also be useful in assessing the efficacy of phototherapy and the potential for kernicterus.