The results of an analysis showed a low correlation between C-reactive protein and procalcitonin in patients with acute respiratory infections.

Marc Meili, from the University Department of Medicine at Kantonsspital Aarau in Switzerland, and colleagues used clinical and biomarker data from 458 (60% women) primary care patients with a pneumonic or non-pneumonic acute respiratory infection (ARI) enrolled in the procalcitonin (PCT) guided antibiotic use versus a standard approach for acute respiratory tract infections in primary care (PARTI) trial between December 2004 and April 2006.

Patients were median 45 years with 40% having upper ARI, such as acute rhinosinusitis or acute pharyngitis/tonsillitis, and 45% having lower ARI, such as acute bronchitis or pneumatic lower respiratory tract infection. Meili and colleagues determined PCT “using a centralized time-resolved amplified cryptate emission technology-based assay with a 0.06 ?g/L functional sensitivity,” while C-reactive protein (CRP) concentrations “were determined by an enzyme immunoassay having a detection limit < 5 mg/dL,” according to the study.

Within the overall population, there was a low correlation between CRP and PCT (r2 = 0.16), with a lower correlation among patients with non-pneumatic ARI (r2 = 0.08) and a higher correlation among patients with pneumatic lower ARI (r2 = 0.34), according to the abstract. Across well-established cut-off ranges, 42% of patients were in similar cut-off ranges, 9% of patients were in higher PCT ranges and 49% of patients were in higher CRP ranges; at 7-day follow-up, 76% of patients were in similar cut-off ranges, 13% were in higher PCT ranges and 11% were in higher CRP ranges, with similarly low correlations when considering changes in baseline to 7-day follow-up. Patients were more likely to have a larger number of restricted days if they had high baseline levels of CRP (> 100 mg/dL, regression coefficient = 1.6; 95% CI, 0.5-2.6) and PCT (> 0.5ug/L, regression coefficient = 2.0; 95% CI, 0.0-4.0), but researchers noted there was no association between discomfort at 14 days and either CRP or PCT, according to a sociodemographic adjusted model.

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