An automated kinetic method to determine creatinine in serum with the Jaffe reaction is described. The method does not require deproteinization or adsorption of creatinine on Fuller9s earth or ion-exchange resin. A maximum of 29 serum samples, standards, and control sera can be assayed in less than 1.5 min. Interferences by most of the known Jaffe-positive serum constituents were studied and minimized by optimal selection of the time interval during which the reaction rate was measured. Results of precision studies and correlation with a manual method requiring adsorption of creatinine on ion-exchange resin are reported. Spectroscopic data suggest that the product of reaction between picrate and creatinine is a 1:1 adduct of the two starting molecules.

Automated Reaction-Rate Method for Determination of Serum Creatinine with the CentrifiChem

(1965). Plasma Creatinine Determination A New and Specific Jaffe Reaction Method. Scandinavian Journal of Clinical and Laboratory Investigation: Vol. 17, No. 4, pp. 381-387.

Plasma Creatinine Determination A New and Specific Jaffe Reaction Method

Total chromogen, true, and AutoAnalyzer methods of measuring serum and urine creatinine by the Jaffe reaction were investigated. Some factors influencing this reaction were examined. These included wavelength, blank, linearity, and conditions of color development. Modifications of the three methods were made and their precision, recovery, and sample stability determined. The interference of ketones and glucose were measured. Finally, the values obtained by the three methods on the same samples of serum and urine were compared statistically.

Estimation of Creatinine by the Jaffe Reaction A Comparison of Three Methods

PHYSIOLOGY Creatine is synthesised by the body in a two-step process (Fig. 1) involving the initial synthesis of guanidinoacetate, which takes place in the kidneys, small intestinal mucosa, pancreas, and probably the liver. The reaction between glycine and arginine is catalysed by a transamidase, which is subject to feedback inhibition by increased creatine levels. Guanidinoacetate is transported to the liver where it is methylated to creatine, which then enters the blood to be widely distributed, chiefly to muscle cells, in which it is converted to creatine phosphate-a source of high energy phosphate bonds for the immediate reformation of ATP during muscular contraction. Creatinine is formed by a spontaneous and irreversible conversion from creatine and creatine phosphate. Formation of creatinine is reasonably constant, and about 2% of whole body creatine is so transformed every 24 h. Consequently, creatinine formation also has a direct relationship to total muscle mass and roughly to the body weight. Creatinine production rate therefore remains approximately the same from day to day unless the muscle mass changes. It is not altered significantly by illness, sepsis, trauma or fever, nor by the state of hydration; however, increased protein intake can result in increases in creatinine production of the order of 10%.

https://journals.sagepub.com/doi/pdf/10.1177/000456328602300101

Analytical Reviews in Clinical Biochemistry: The Estimation of Creatinine:

https://www.amjmed.com/article/0002-9343(62)90183-3/pdf

A clinical appraisal of the plasma concentration and endogenous clearance of creatinine.

/pdf/the-determination-of-creatinine-in-plasma-or-serum-and-in-m2ahoqi5v5.pdf

The determination of creatinine in plasma or serum, and in urine; a critical examination.

It is commonly but not unanimously held that the renal clearance of inulin measures the glomerular filtration rate in man, and that creatinine is partly excreted by the renal tubules.



Results obtained from infusion experiments indicate that both substances are excreted at rates proportional to the respective plasma concentrations. The creatinine/inulin clearance ratio is never less than 1.0 and tends to decrease when the concentrations of creatine and inulin are high, sometimes as a result of slight increases in the inulin clearance and more commonly due to slight decreases in the creatinine clearance



The interpretation of these findings is discussed in relation to the problem of the measurement of the glomerular filtration rate in man. It is concluded that there is at present no conclusive evidence in favour of the acceptance of the use of either substance.

F. J. Scandrett

Papers

The determination of creatinine in plasma or serum, and in urine; a critical examination.

The measurement of the glomerular transference rate in man