Effect of various protein precipitants on recoveries of creatinine added to plasma.

NCOMPLETE RECOVERIES OF CREATININE added to plasma or serum have been reported by investigators who have used a tungstic acid protein precipitation and the picric acid method of analysis (1-7). Controversy exists as to whether the creatinine is lost by adsorption on the protein precipitate or whether the alkaline picrate formed in these circumstances is modified so that less color is formed. Owen et al. have reported that both the true and apparent creatinine values were influenced by the reagent used for protein precipitation (1). The true and apparent creatiine values were calculated after using the picric acid method in conjunction with either Lloyd’s reagent, (a hydrated aluminum silicate), or by means of specific creatinine destroying bacteria. In this investigation, recoveries of creatinine added to whole blood and plasma were determined with various types of protein-free filtrates and by the o-nitrobenzaldehyde method of analysis. It was found that complete recoveries of creatine and creatiine added to plasma or whole blood were obtained with the tungstic acid method of protein precipitation. The normal values for creatine and creatinine in whole blood and plasma by the o-nitrobenzaldehyde procedure were compared with those obtained by the picric acid method.