NEW AUTOMATED-METHOD FOR DETERMINATION OF TRUE CREATININE IN SERUM BY MEANS OF CENTRIFICHEM CENTRIFUGAL ANALYZER, BASED ON SLOTS PRINCIPLE - WITH SPECIAL REFERENCE TO LOW SUBSTRATE CONCENTRATIONS

A new automated method is proposed for the accurate determination of the true creatinine concentration in 20 μl serum, based on the measurement of the initial rate of the decomposition reaction of the creatinine picrate complex caused by decreasing the pH. The results of this method, performed with a Centrifichem® centrifugal analyzer system (type 300 F), are compared with the results obtained by two other methods: a manual method based upon the adsorption on Fuller's earth, and the Auto Analyzer method. In these comparative studies special attention is paid to the analysis of sera containing low (normal) substrate concentrations. Calculation of the orthogonal regression between the results obtained by the adsorption method (x) and the proposed method (y) gave: y = 0.97 x ± 5 μmol/l ( x ̄ = 91.3 μmol/l, y ̄ = 93.5 μmol/l), while for the correlation coefficient (r) 0.9721 was found. All sera (n = 113) had creatinine concentrations between 40 and 180 μmol/l. © 1978.