title: Refinement of the association of serum C-reactive protein concentration and coronary heart disease risk by correction for within-subject variation over time: the MONICA Augsburg studies, 1984 and 1987.
abstract: The authors sought to assess the repeatability of measurements of C-reactive protein, an independent predictor of coronary heart disease, in a large cohort of apparently healthy men and to correct earlier estimates of the association of C-reactive protein and coronary heart disease for the measurement error in this protein. They measured C-reactive protein by a high-sensitivity assay in 936 men aged 45-64 years in the MONICA (Monitoring of Trends and Determinants in Cardiovascular Disease) Augsburg cohort in 1984-1985 and remeasured it 3 years later. All men were subjected to an 8-year follow-up of their cardiovascular status. The analytical variation of the assay was small, with the analytical variance component at 1 percent of the within-subject variance component, a repeatability coefficient of 25 percent, and a reliability coefficient of 1.00. In contrast, the within-subject variation of C-reactive protein corresponded to a repeatability coefficient of 740 percent and a reliability coefficient of 0.54, indicating considerable within-subject variation. Based on the authors' estimates, three serial determinations of C-reactive protein should be done to achieve a reliability of 0.75, the value they found for total cholesterol. Correcting the hazard ratios in their original analysis of the association of coronary heart disease and high-sensitivity-assay C-reactive protein for the measurement error in C-reactive protein and covariables leads to a considerably larger estimate. The results suggest that the true association between C-reactive protein and cardiovascular risk is underestimated by a single C-reactive protein determination, and that several serial C-reactive protein measurements should be taken.
authors.affiliation: Department of Internal Medicine II-Cardiology, University of Ulm Medical Center, Robert-Koch-Strasse 8, D-89081 Ulm, Germany. wolfgang.koenig@medizin.uni-ulm.de
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Koenig
authors.forename: Malte
authors.initials: M
authors.lastname: Sund
authors.forename: Margit
authors.initials: M
authors.lastname: Fröhlich
authors.forename: Hannelore
authors.initials: H
authors.lastname: Löwel
authors.forename: Winston L
authors.initials: WL
authors.lastname: Hutchinson
authors.forename: Mark B
authors.initials: MB
authors.lastname: Pepys
mesh_terms: D015415:Biomarkers / Q000097:blood*; D002097:C-Reactive Protein / Q000032:analysis*; D003327:Coronary Disease / Q000097:blood*; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results
chemical_list: D015415:Biomarkers; D002097:C-Reactive Protein