Determination of serum bilirubin concentration during phototherapy of newborns and in vitro: results compared by the direct spectrometric method and the diazo method.

During direct illumination of a serum bilirubin solution the bilirubin concentration decreased markedly, both as determined by the direct spectrometric method and (even more so) by the diazo method. In contrast, I found the same values for serum bilirubin concentrations as determined by these two methods for serum from untreated, "single light", and "double light" treated full-term infants with neonatal hyperbilirubinemia without blood type immunization. The same was true for untreated and "single light" treated premature infants with this disease. Furthermore, no difference was found in the above-mentioned relationship between "single light" treated infants with the same disease, and untreated infants with neonatal hyperbilirubinemia without immunization, all born at term. This is important, because the direct spectrometric method is simpler and requires less serum than does the diazo method.