Evaluation of a predictive kinetic procedure for the enzymatic measurement of creatinine in serum.
We have evaluated the analytical performance of a predictive kinetic procedure for the enzymatic measurement of serum creatinine in comparison with equilibrium and kinetic fixed-time procedures. The procedure uses commercially available reagents and is based on calculating the total change in absorbance expected if the reaction were to proceed to equilibrium by fitting the initial part of the absorbance-time curve to a three-parameter function by non-linear regression. Total imprecision for different concentrations of creatinine ranges from 1.47 to 1.86% and is significantly better than that obtained for the fixed-time procedure. The results with the predictive procedure are less dependent on creatinine amidohydrolase activity in the reagent, pH of the reagent and temperature of analysis than are the results with the fixed-time procedure. All the procedures are interfered with by bilirubin and ascorbic acid to about the same extent. Recovery and linearity are quite acceptable, and the estimated accuracy is below 2.1%. However, in comparison with the equilibrium procedure, the predictive procedure tends to underestimate creatinine concentrations at values below 100 micromol/l, and the results obtained by the two procedures are not transferable. In conclusion, the predictive approach substantially improves the imprecision but not the specificity of the enzymatic assay of serum creatinine.
Yago
M
M
Laboratorio de Bioquímica, Hospital General, Castellón, Spain.
José Olmos
M
M
Gómez
T
T
D016477:Artifacts; D003404:Creatinine / Q000097:blood*; D005069:Evaluation Studies as Topic; D006801:Humans; D011237:Predictive Value of Tests; D015203:Reproducibility of Results
D003404:Creatinine