Creatine and Creatinine in Whole Blood and Plasma

The methods elaborated by Folk’ for the determination of small quantities of creatine and creatinine have been of great service in quantitative investigations involving these compounds, and the numerous criticisms and modifications suggested as improvements on the original technique are sufficient, evidence of their widespread use. But recent discussions2s 3, 4 have disclosed several possible sources of error which have been sufficiently emphasized to prevent further confusion. During the last year we have been interested in the estimation of creatine and creatinine in blood and have encountered several of the difficulties described in recent communications. With these obstacles overcome to our satisfaction, we have determined preformed and total creatinine both in whole blood and in plasma from different animal species, using the original method of Folin and, at the same time, another procedure for total creatinine which we shall describe. Comparisons of the two methods have indicated that the method of Folin may yield inaccurate results for total creatinine, at least when applied to whole blood. The differences observed between the concentrations of ereatine in whole blood and plasma from human beings as determined by the newer method emphasize the importance of such differentiation in studies whose object is to correlate the quantities of the