Excellent agreement between C-reactive protein measurement methods in end-stage renal disease patients--no additional power for mortality prediction with high-sensitivity CRP.

BACKGROUND

The conventional method for C-reactive protein (CRP) measurement is an immunoturbidimetric assay (imCRP, detection limit > or =3 mg/l). However, high-sensitivity CRP (hsCRP, detection limit >0.1 mg/l) has been advocated as preferable biomarker for cardiovascular risk assessment. The aim of this study was to determine agreement between imCRP and hsCRP in end-stage renal disease (ESRD) patients, and to examine whether the association between CRP and mortality is comparable when using imCRP or hsCRP.

METHODS

Patients from a prospective follow-up study among incident ESRD patients (NECOSAD) with serum CRP available at 3 months of follow-up were included [n = 840, 60% male, mean (SD) age 59 (15) years]. Agreement between imCRP and hsCRP was determined by intraclass correlation coefficient (ICC) and by Cohen's kappa (kappa) for CRP dichotomized to the presence (CRP >10 mg/l) or absence of systemic inflammation. The association between CRP and mortality was determined by Cox regression analysis and c-statistic.

RESULTS

ICC between imCRP and hsCRP was 0.78, which improved to 0.86 after correction for systematic differences between measurement methods. Systemic inflammation was present in 28.2% and absent in 67.6% of patients according to both methods (discordant in 4.2%), resulting in good agreement between the two methods (kappa = 0.90). Patients with systemic inflammation had a significantly increased mortality risk compared with patients without systemic inflammation [HR(im,adj) = 1.49 (95%CI 1.14-1.93) and HR(hs,adj) = 1.53 (1.18-2.0)]. Predictive capacity of mortality was similar for both CRP methods [c-statistic(adj) 0.83 (0.79-0.86)].

CONCLUSION

The agreement between imCRP and hsCRP in patients with ESRD is very good. Furthermore, the association between CRP and mortality in ESRD patients is similar when using imCRP and hsCRP. These data suggest that there is no need to use a high-sensitivity method for the determination of inflammatory status in ESRD patients.