title: Creatinine in urine - a method comparison.
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.
authors.affiliation: Institute of Forensic Medicine, University of Bern, Bühlstrasse 20, 3012, Bern, Switzerland.
authors.forename: Marc
authors.identifier: http://orcid.org/0000-0002-3111-0750
authors.initials: M
authors.lastname: Luginbühl
authors.affiliation: Institute of Forensic Medicine, University of Bern, Bühlstrasse 20, 3012, Bern, Switzerland.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Weinmann
mesh_terms: D002853:Chromatography, Liquid / Q000379:methods; D003404:Creatinine / Q000652:urine*; D006801:Humans; D057230:Limit of Detection; D019095:Point-of-Care Systems; D013053:Spectrophotometry / Q000379:methods; D015813:Substance Abuse Detection / Q000379:methods; D053719:Tandem Mass Spectrometry / Q000379:methods; D016482:Urinalysis / Q000379:methods*; D059349:Urine Specimen Collection / Q000379:methods
chemical_list: D003404:Creatinine
keywords: creatinine; drug testing; point-of-care testing; urine analysis; urine manipulation