Automated determination of urinary creatinine without sample dilution: theory and practice

Area of Science:

• Clinical Chemistry
• Analytical Chemistry
• Biochemistry

Background:

• The Jaffé reaction is a common method for creatinine determination.
• The reaction rate is influenced by sodium hydroxide concentration.
• Existing automated methods may require manual sample dilution.

Purpose of the Study:

• To develop and validate an automated method for direct urinary creatinine determination.
• To optimize the Jaffé reaction conditions for automated analysis.
• To compare the new method with established automated analyzers.

Main Methods:

• An automated kinetic assay was developed using the Jaffé reaction.
• Optimized conditions included 10 mmol/L picrate, 60 mmol/L sodium hydroxide, and a 1:41 sample to final volume ratio at 37°C.
• Measurements were taken at 500 or 510 nm between 30 and 90 seconds.

Main Results:

• The automated method provided results comparable to the AutoAnalyzer and aca.
• Run-to-run coefficients of variation (CVs) were 3.6% or less.
• The method demonstrated accuracy for creatinine concentrations up to 3000 mg/L.

Conclusions:

• The developed automated method allows for direct urinary creatinine determination without manual dilution.
• This method is a suitable and accurate replacement for the AutoAnalyzer and aca.
• The optimized Jaffé reaction offers a reliable approach for routine clinical analysis.