Automated determination of urinary creatinine without sample dilution: theory and practice.
The rate of the Jaffé reaction depends on the concentration of sodium hydroxide; the pseudo-first-order rate constant of the reaction, at 37 degrees C in 10 mmol/L picrate solution, is 0.004 mmol/L. We formulated an automated method to determine urinary creatinine directly without manual sample dilution. The conditions are as follows: 10 mmol/L picrate and 60 mmol/L sodium hydroxide (final concentrations); ratio of sample to final volume, 1:41; temperature, 37 degrees C; wavelengths of measurement, 500 or 510 nm; interval of measurement, 30 to 90 s; and mode of measurement, kinetic. Determinations of creatinine in patients' samples by the new method compared favorably with those obtained with the AutoAnalyzer and aca. The run-to-run CVs were 3.6% or less, and the method was accurate for concentrations of creatinine up to 3000 mg/L. We recommend this method as a good replacement for the AutoAnalyzer or aca methods.
D001322:Autoanalysis / Q000379:methods; D002440:Cefoxitin; D002512:Cephalothin; D003404:Creatinine / Q000652:urine*; D006801:Humans; D007202:Indicators and Reagents; D007700:Kinetics; D008433:Mathematics; D012972:Sodium Hydroxide
D007202:Indicators and Reagents; D012972:Sodium Hydroxide; D002440:Cefoxitin; D003404:Creatinine; D002512:Cephalothin