An international assessment of the metrological equivalence of higher-order measurement services for creatinine in serum |
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Authors: | Camara Johanna E Lippa Katrice A Duewer David L Gasca-Aragon Hugo Toman Blaza |
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Institution: | (1) Analytical Chemistry Division, National Institute of Standards and Technology (NIST), 100 Bureau Drive, MS 8392, Gaithersburg, MD 20899-6392, USA;(2) Department of Mathematics & Statistics, University of Massachusetts, Amherst, MA 01003-9305, USA;(3) Statistical Engineering Division, National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899-8980, USA |
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Abstract: | The Consultative committee for amount of substance-metrology in chemistry (CCQM)-K80 Key Comparison directly assessed the
equivalence of many of the world’s higher-order value-assigned materials (HOVAMs) for creatinine in human serum. This 2009
international study compared the certified values and uncertainties of the materials using measurements made under repeatability
conditions. The study evaluated 17 materials submitted by 6 national metrology institutes (NMIs). The creatinine quantity
in these materials ranged from 3 mg/kg to 57 mg/kg (about 0.3 mg/dL to 6 mg/dL or 30 nmol/L to 500 nmol/L). All materials
were stored and prepared according the specifications provided by the participating NMIs. Samples were processed and analyzed
under repeatability conditions by one analyst using isotope-dilution liquid chromatography–mass spectrometry in two measurement
campaigns. The certified values and repeatability measurements were compared using uncertainty-weighted generalized distance
regression. The instrumental repeatability relative standard deviation was 1.2%. The measurement design required assessment
of within-unit and between-campaign variability in addition to measurement repeatability. At a 95% level of confidence, the
certified values for all 17 materials agreed to within their assigned uncertainties. CCQM-K80 demonstrated the metrological
equivalence of the currently available HOVAMs for creatinine in human serum and of the creatinine measurement services provided
by the participating NMIs. |
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