Refinement of the Association of Serum C-reactive Protein Concentration and Coronary Heart Disease Risk by Correction for Within-Subject Variation over Time

• Published in: American journal of epidemiology Vol. 158; no. 4; pp. 357 - 364
• Main Authors: Koenig, Wolfgang, Sund, Malte, Fröhlich, Margit, Löwel, Hannelore, Hutchinson, Winston L., Pepys, Mark B.
• Format: Journal Article
• Language: English
• Published: Oxford University Press 15.08.2003
• Subjects: analytical variance component; between-subject variance component; confidence interval; coronary disease; inflammation; MONICA; Monitoring of Trends and Determinants in Cardiovascular Disease; predictive value of tests; proteins; VCa; VCb; VCw; within-subject variance component
• ISSN: 0002-9262; 1476-6256
• DOI: 10.1093/aje/kwg135

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.