| Abstract: | 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 liquid chromatography–tandem mass spectrometry (LC–MS/MS) method, a spectrophotometric method on an AU 480 chemistry system, and a portable, chemical‐reaction‐based, point‐of‐care testing device were 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 slightly overestimates 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, for example by dilution of the sample. Copyright © 2017 John Wiley & Sons, Ltd. |
