Direct spectrophotometry of bilirubin in serum of the newborn, with use of caffeine reagent.

We recently described a direct spectrophotometric method for unconjugated bilirubin, with caffeine reagent (Clin Chem 1986;32:1389-93). Because this method is independent of the protein matrix we used it for the preparation of bilirubin standards (Clin Chem 1987;33:1817-21). Now, in this paper, we utilize the caffeine reagent in setting up a bilirubin method for serum from neonates. This resulted in a two-wavelength (465 and 528 nm) equation, which fully corrects for HbO2 interferences. In combination with a bilirubin standard, this equation may be transformed into a simple relative formula for use with this simple dilution method. We studied this two-wavelength method with 55 neonates' sera, comparing results with those by both the diazo method of Doumas et al. (Clin Chem 1985;31:1779-89) and the borate method of Hertz et al. (Scand J Clin Lab Invest 1974;33:215-30). We found that this new method is independent of hemolysis and of the matrix of the sera. Therefore, it is very suitable for use in neonatology.