sodium-nitrite and diazobenzenesulfonic-acid

We describe an improved colorimetric method for assays of total and direct bilirubin in serum. Bilirubin reacts with diazotized sulfanilic acid in an acidic medium to form a blue azopigment. Total bilirubin is assayed in the presence of reaction accelerators (caffeine, urea, and citric acid), direct bilirubin in their absence. The azo compound so formed is read at the same wavelength (570 nm) in both assays. A sample blank is run in parallel. Standard curves are linear for total and direct bilirubin concentrations up to 513.0 and 256.5 mumol/L, respectively. The method is characterized by (a) use of the same protocol for both assays, i.e., a one-step procedure with short reaction time (5 min at room temperature), and (b) use of a single working solution, which, refrigerated, is stable for one month. The method is reliable, yields results that compare closely with those of the classical Jendrassik--Gróf method, is suitable for routine use, and lends itself to automation.

Topics: Bilirubin; Caffeine; Citrates; Citric Acid; Colorimetry; Diazonium Compounds; Hemoglobins; Humans; Hydrogen-Ion Concentration; Hyperlipidemias; Indicators and Reagents; Kinetics; Quality Control; Sodium Nitrite; Spectrophotometry; Sulfanilic Acids; Urea

To assess notably high measurements of direct bilirubin in the serum of newborns obtained on the DuPont aca analyzer, the authors compared results from the aca instrument with the results from the Technicon RA-1000 analyzer. Total and direct bilirubin values in 11 serum samples of newborn babies were measured in parallel on both instruments. There was good correspondence between the two instruments in determination of total bilirubins. However, the diazotized sulfanilic acid method (used by both instruments) yielded much higher direct bilirubin values on the aca analyzer than on the RA-1000. The possibly spuriously elevated direct bilirubin results produced by the aca may cause clinical confusion.

Topics: Bilirubin; Blood Chemical Analysis; Diazonium Compounds; Humans; Infant, Newborn; Osmolar Concentration; Sodium Nitrite; Sulfanilic Acids