B-070 Quantification of Urine Creatine and Creatinine by Vantera® NMR Clinical Analyzer

Background Creatine is a substance that the body uses to produce energy. The creatine concentration in urine is widely used as a tool to diagnose creatinuria. Urine creatinine is used to identify patients at risk of recurrent nephrolithiasis or kidney stones, and commonly serves as a means to normalize the concentrations of other metabolites in urine. Here we describe the development of a low cost, high-throughput nuclear magnetic resonance spectroscopy (NMR)-based assay to simultaneously measure urine creatine and creatinine. Methods The NMR samples are tested on the Vantera® Clinical Analyzer, a 400MHz NMR instrument designed specifically for the clinical laboratory. The NMR data are automatically transferred and processed. Urine creatinine was quantified as reported previously while creatine concentrations were determined using a newly developed non-negative deconvolution algorithm that utilized both of its NMR signal peaks. Results Deming regression analysis comparing creatine and creatinine concentrations in urine between NMR and chemistry methods were conducted. The linearity was observed over a wide range of concentrations for creatine (up to 100 mg/dL) and creatinine (up to 1,308 mg/dL). In a population of apparently healthy adults, the estimated reference interval for creatine was < 10 mg/dL and the reported reference interval for creatinine was < 174.5 mg/dL. The linearity of our assay was established well beyond these intervals. In addition, the new algorithm, by using the combination of two NMR peaks of creatine, provided a more stable model to tolerate underlying signals from potential interfering substances. Conclusion The newly developed NMR-based high-throughput assay exhibited excellent performance characteristics to quantify the creatine and creatinine in urine for clinical diagnostic purposes. It showed results comparable to the currently utilized chemistry tests and provides a useful tool to simultaneously measure the creatine and creatinine in urine for clinical and research use.