Determination of inflammatory biomarkers in patients with COPD: a comparison of different assays

CRP and SAA concentrations measured by ELISA and nephelometry in 88 patients with COPD and 45 control subjects were used to evaluate the performance of these methods in a clinical setting.With both assays, the concentrations of CRP and SAA were higher in COPD patients than in controls after adjustment for age and sex. There was a moderate correlation between the values measured by ELISA and those measured by nephelometry (logCRP: r = 0.55, p < 0.001; logSAA: r = 0.40, p < 0.001). However, the concentrations of biomarkers determined by nephelometry were significantly higher than those obtained with ELISA for CRP (mean difference = 2.7 (9.4) mg/L) and SAA (mean difference = 0.31 (14.3) mg/L).Although the serum CRP and SAA concentrations measured by ELISA and nephelometry correlated well in COPD patients, the ELISA values tended to be lower for CRP and SAA when compared with nephelometric measurements. International standardization of commercial kits is required before the predictive validity of inflammatory markers for patients with COPD can be effectively assessed in clinical practice.Chronic obstructive pulmonary disease (COPD) is a complex chronic inflammatory disease of the lungs with significant extrapulmonary effects that may contribute to its severity in individual patients [1,2]. Growing evidence suggests that markers of systemic inflammation, such as C-reactive protein (CRP) and serum amyloid A (SAA), are increased in patients with COPD compared with control subjects without COPD [3]. For this reason, low-grade systemic inflammation is currently considered to be a hallmark of COPD and one of the key mechanisms that may be responsible for the increased rate of comorbidity.CRP is the prototypic acute-phase reactant that belongs to the highly conserved pentraxin family of plasma proteins. Current evidence indicates that increased CRP levels can be used to identify subjects who have an increased risk of developing myocardial infarction, stroke, unstable angina, o