Automated measurement of urinary creatinine by multichannel kinetic spectrophotometry

Urinary creatinine analysis is required for clinical diagnosis, especially for evaluation of renal function. Creatinine adjustment is also widely used to estimate 24-h excretion from spot samples. Few convenient validated approaches are available for in-house creatinine measurement for small- to medium-scale studies. Here we apply the Jáffe reaction to creatinine determination with zone fluidic multichannel kinetic spectrophotometry. Diluted urine sample and reagent, alkaline picric acid, were mixed by a computer-programmed dispenser and rapidly delivered to a four-channel detection cell. The absorbance change was monitored by a flow-through light-emitting diode-photodiode-based detector. Validation results against high-performance liquid chromatography-ultraviolet (HPLC-UV)/mass spectrometry (MS) are presented. Responses for 10-fold diluted samples were linear within clinically relevant ranges (0-250 mg/L after dilution). The system can analyze 70 samples per hour with a limit of detection of 0.76 mg/L. The relative standard deviation was 1.29% at 100 mg/L creatinine (n=225). Correlation with the HPLC (UV quantitation/MS confirmation) system was excellent (linear, r2=0.9906). The developed system allows rapid, simple, cost-effective, and robust creatinine analysis and is suitable for the analysis of large numbers of urine samples.