DETERMINATION OF SERUM BILIRUBIN BY SKIN REFLECTANCE - EFFECT OF PIGMENTATION

A noninvasive optical technique by which serum bilirubin can be estimated from skin spectral reflectance measurements has been further investigated. The original work on 30 healthy, full-term white infants and an independent study on 14 white and 30 black infants demonstrate that the method has potential not only for clinical use, but also for the study of the transport of bilirubin to, from and within the skin. The objectives of the present study are to evaluate the method on a larger sample population with special attention to natural skin pigmentation effects and the development of a physical model of the tissue to explain the relationship between serum bilirubin concentration and skin reflectance. Reflectance spectra (380-800 nm) and concurrent serum bilirubin measurements were taken on a sample population of 58 white and 45 full-term black infants (1-3 days of age). Multiple linear regression analysis, comprised of six wavelengths gave a correlation coefficient, r = 0.831 for the white infant group. For the black infant group, a five wavelength analysis provided r = 0.877 with the standard error of estimate being ±1.46 mg/100 ml for both groups. The model for establishing a physical basis for the relationship shows that a transformed, normalized Kubelka-Monk function £ (460, 510, 420) is linearly related to serum bilirubin concentration. This function is determined from the spectral reflectance values at three wavelengths, 420, 460, and 510 nm. The wavelength combination is such that effects due to hemoglobin and melanin pigments are minimized. Regression analysis showed that r = 0.778 and r = 0.865 for the white and black infant groups, respectively, with standard error of estimates being ±1.4 mg/100 ml for both groups. Routine determinations of total serum bilirubin by laboratory methods have standard errors of estimate ranging from ±1 to 1.5 mg/100 ml. Thus, the method herein described shows that the relationship between skin reflectance and serum bilirubin in full- term infants is close to the acceptable limits for clinical use. Furthermore, this work shows that skin pigmentation does not obscure this relationship. Speculation: Because skin pigmentation does not obscure the relationship between serum bilirubin and spectral reflectance, the latter is clinically useful for jaundice screening for all neonates. It may also be helpful in monitoring phototherapy of jaundiced infants although the spectral considerations may be extremely complex in these cases. Once such relationships are determined, however, skin reflectance may also offer a measure of the risks of kernicterus. © 1979 International Pediatric Research Foundation, Inc.