Simple Automated Method for Urinary Creatinine Estimation.

The increasing numbers of investigations into metabolic processes have necessitated the adaptation to automated principles of a method whereby the efficacy of quantitative urine collections can be tested. The estimation of creatinine (creatine anhydride) for this purpose has several aJvantages over other methods which have been used. Creatinine excretion is fairly constant from day to day (Folin, 1914; Shaffer, 1914), being independent of muscular activity, urine volume, and the state of nitrogen metabolism of the body. Creatinine is a waste product endogenously derived from creatine and its level of excretion is influenced by the diet only when the diet contains significant quantities of creatine or creatinine, for example, in a heavy fish or meat meal. When preformed creatinine is administered to normal subjects it is rapidly and almost wholly excreted. Thus, it can be seen that if marked variations in urinary creatinine levels are observed which do not correspond to muscular development or breakdown, or to changes in the diet involving preformed creatinine, it can be assumed that there has been some error in the collection of urine specimens. The main criteria of the method for urinary creatinine estimation were that it should be rapid, accurate, and basically simple in both design and operation. The method which has been evolved is operated at a rate of 60 estimations per hour, can estimate specimens containing creatinine concentrations of 0-200 mg./100 ml., and is based on the Jaffe (1886) reaction. The Jaffe reaction takes place when creatinine is mixed with alkaline picrate solution giving rise to the formation of the red tautomer of creatinine picrate (Greenwald and Gross, 1924; Greenwald, 1925, 1928). The known lack of specificity of the reaction for plasma has not been held to invalidate its use in urine estimations. The coloured product formed obeys Beer's law for monochromatic