Quantitation of sputum protein by use of the biuret reaction.

A simple, accurate method is described for quantitatively determining the protein content of sputum by use of the biuret reaction. Fitteen mechanically homogenized specimens were examined with the biuret reagent described by Rosenthal and Cundiff, and the results compared with those obtained by the microKjeldahl technique. Over a range of 542 to 1917 mg of protein per 100 ml, the techniques correlated significantly. Difficulties with deproteinization of the sputum before nonprotein nitrogen was determined were overcome by the use of zinc sulfate and pH adjustment. The proposed method is fast and reproducible.