Interference of sodium azide with the quantitation of bilirubin: modification of Fog's method to eliminate azide interference.

Interference of sodium azide with bilirubin estimation was studied at different concentrations of sodium azide. At an azide concentration (0.08% or 12.3 mM), 99% inhibition of the color reaction was observed. Similar results were obtained when the effect of sodium azide was studied by fixing bilirubin concentration and increasing the azide concentration. The decrease in color reaction can be explained on the basis of competition of the two compounds, i.e., bilirubin and sodium azide for diazosulfanilic acid. The method was modified to measure the concentration of bilirubin in various serum samples containing different amounts of sodium azide.