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. 2013 Apr 8;8(4):e60759.
doi: 10.1371/journal.pone.0060759. Print 2013.

Time variability of C-reactive protein: implications for clinical risk stratification

Peter Bogaty  1 , Gilles R Dagenais, Lawrence Joseph, Luce Boyer, Anne Leblanc, Patrick Bélisle, James M Brophy
Affiliations

Time variability of C-reactive protein: implications for clinical risk stratification

Peter Bogaty et al. PLoS One. .

Abstract

Background: C-reactive protein (CRP) is proposed as a screening test for predicting risk and guiding preventive approaches in coronary artery disease (CAD). However, the stability of repeated CRP measurements over time in subjects with and without CAD is not well defined. We sought to determine the stability of serial CRP measurements in stable subjects with distinct CAD manifestations and a group without CAD while carefully controlling for known confounders.

Methods: We prospectively studied 4 groups of 25 stable subjects each 1) a history of recurrent acute coronary events; 2) a single myocardial infarction ≥7 years ago; 3) longstanding CAD (≥7 years) that had never been unstable; 4) no CAD. Fifteen measurements of CRP were obtained to cover 21 time-points: 3 times during one day; 5 consecutive days; 4 consecutive weeks; 4 consecutive months; and every 3 months over the year. CRP risk threshold was set at 2.0 mg/L. We estimated variance across time-points using standard descriptive statistics and Bayesian hierarchical models.

Results: Median CRP values of the 4 groups and their pattern of variability did not differ substantially so all subjects were analyzed together. The median individual standard deviation (SD) CRP values within-day, within-week, between-weeks and between-months were 0.07, 0.19, 0.36 and 0.63 mg/L, respectively. Forty-six percent of subjects changed CRP risk category at least once and 21% had ≥4 weekly and monthly CRP values in both low and high-risk categories.

Conclusions: Considering its large intra-individual variability, it may be problematic to rely on CRP values for CAD risk prediction and therapeutic decision-making in individual subjects.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Display of all CRP values of subjects with recurrent acute coronary events.
Figure 2
Figure 2. Display of all CRP values of subjects with a single remote myocardial infarction (MI).
Figure 3
Figure 3. Display of all CRP values of subjects with longstanding always stable coronary artery disease (CAD).
Figure 4
Figure 4. Display of all CRP values of subjects without coronary artery disease (CAD).
Figure 5
Figure 5. Numbers of subjects (and %) changing CRP risk category from one measurement to the next by weekly (top), monthly (middle), and tri-monthly (bottom) intervals.
Figure 6
Figure 6. Probability of error in risk category assignment based on any assumed to be ‘true’ CRP measurement.
See this image and copyright information in PMC

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