title: Evaluating an alternative method for rapid urinary creatinine determination.
abstract: Creatinine (CR) is an endogenously produced chemical that is routinely assayed in urine specimens to assess kidney function and sample dilution. The industry-standard method for CR determination, known as the kinetic Jaffé (KJ) method, relies on an exponential rate of a colorimetric change, and can therefore require automated processing equipment for moderate- to high-throughput analysis (hundreds to thousands of samples per day). This study evaluates an alternative colorimetric method, the "plateau Jaffé" (PJ) method, which utilizes the chemistry of the KJ method, a commercially available kit, and a multipoint calibration curve. This method is amenable to moderate-throughput sample analysis and does not require automated processing equipment. Thirty-two spot urine samples from healthy adult volunteers were analyzed for creatinine concentration (CRc) using the KJ and PJ methods. Samples were also analyzed using a liquid chromatography time-of-flight mass spectrometry (LC-TOF/MS) method, which acted as an analytical control. Replicate measurements of spot samples (natural log-transformed values) were used to estimate method precision, and linear regression models were used to evaluate method accuracy (LC-TOF/MS measurements were considered the analytical benchmark). Measurement precision was comparable across all three methods, with coefficent of variation estimates ranging from 3 to 6%. Regression models generally showed good agreement across methods with R(2) estimates ranging from .996 to .998, slope estimates ranging from .944 to .986, and y-intercept estimates ranging from 0.111 to 0.303. Minor bias (between 2 and 16%) was observed across methods at the tails of the measurement distributions. The provided regression equations can be used to adjust for this bias and to improve CR measurement comparisons across studies employing different methods. Considering these results, the PJ method is a suitable alternative to the industry standard KJ method for urinary CRc determination. It can be implemented for moderate-throughput sample analysis using modest and commonly available lab instrumentation and manual sample preparation techniques.
authors: a Human Exposure and Atmospheric Sciences Division , National Exposure Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency , Research Triangle Park , North Carolina , USA.
authors: Erik M
authors: EM
authors: Andersen
authors: Jon R
authors: JR
authors: Sobus
authors: Mark J
authors: MJ
authors: Strynar
authors: Joachim D
authors: JD
authors: Pleil
authors: Shoji F
authors: SF
authors: Nakayama
mesh_terms: D000328:Adult; D002138:Calibration; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D003404:Creatinine / Q000652:urine*; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D013058:Mass Spectrometry / Q000379:methods*; D008875:Middle Aged; D055815:Young Adult
chemical_list: D003404:Creatinine