Creatinine in urine - a method comparison.

Luginbühl, Marc; Weinmann, Wolfgang (2017). Creatinine in urine - a method comparison. Drug testing and analysis, 9(10), pp. 1537-1541. Wiley 10.1002/dta.2166

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Drug screening in urine is widely applied in forensic toxicology. Contrary to blood analysis, excessive or reduced fluid intake can substantially alter the concentration of substances in urine. As a standard to detect urinary dilution, creatinine concentrations are analyzed. A sample with a concentration below 20 mg/dL is generally defined as too diluted to provide a valid result in abstinence control samples. This work investigates the potential of three different methods for the determination of creatinine concentrations in urine samples: A ZIC-HILIC based LC-MS/MS method, a spectrophotometric method on an AU 480 chemistry system, and a portable, immunoassay based point-of-care testing device was compared by measuring 200 urine samples. When comparing the two laboratory methods, LC-MS/MS and spectrophotometry, a mean difference of 3.7 ± 14 mg/dL was found, indicating that the spectrophotometric method is slightly overestimating the creatinine concentration. When comparing the LC-MS/MS method with the point-of-care testing device, a mean concentration difference within the calibration range for POCT (>20 mg/dL (excluding 16 samples) and <500 mg/dL (excluding 4 samples)) of 21 ± 37 mg/dL was found, indicating that the point-of-care testing device overestimates the measured creatinine concentration. A point-of-care testing device as used during this study can provide valuable information for on-site analysis. However, reported concentrations above 500 mg/dL should be further evaluated e.g. by dilution of the sample.

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