[Fundamental studies on transcutaneous bilirubinometry in newborn infants using an organ scanning spectrophotometer]

In vivo reflectance spectra in the visible region were recorded on the blanched skin on the foreheads, chests, arms and legs of 140 newborn infants using an organ scanning spectrophotometer, and corresponding total serum bilirubin levels were determined. An elevation in the absolute spectra was observed in the 460 nm region for the higher bilirubin level, and the isosbestic point was located in the 510 nm region. A linear relationship was observed between the reflectance spectra difference and the serum bilirubin level. Although the best analysis results were obtained from the measurements of the reflectance spectra difference between 460 nm and 510 nm on the chests (r = 0.954, Y = 40.62X + 1.36), or on sums of 4 measuring sites (r = 0.973, Y = 46.59X + 0.61), there was no statistical difference from the values obtained between 460 nm and 550 nm on the foreheads (r = 0.913, Y = 33.55X + 5.30). The slopes and the Y-intercepts of the linear regressions differed considerably at various measuring sites. Marked decreases in the reflectance spectra differences were observed during the phototherapies and prominent rebounds followed for 24 hours after the cessation of phototherapies. The noninvasive and simple reflectance method was sensitive to the bilirubin level in the tissue and might be a better indicator of neonatal risk of kernicterus. However, the optical method has a certain limitations in representing the bilirubin concentration in the blood stream, especially during, and for 24 hours, after phototherapies.