Procalcitonin, C-reactive protein, and cell counts in the diagnosis of parapneumonic pleural effusions.

Background And Objective: Pleural effusion is relatively common in pneumonia. Because traditional methods for its diagnosis are not always effective, there is a need for new biomarkers to make its differential diagnosis easier.

Methods: A total of 233 patients with pleural effusion were admitted to our hospital between 2005 and 2008. Total and differential leukocyte counts, along with blood and pleural fluid procalcitonin and C-reactive protein (CRP) were performed on all of them. The patients were classified into 5 groups depending on the cause of their effusion: (1) parapneumonic, n = 28; (2) tuberculous, n = 49; (3) neoplastic, n = 57; (4) miscellaneous, n = 46; and (5) transudates, n = 53.

Results: Procalcitonin levels were higher in the pleural fluid of the parapneumonic group (PAR, 0.15 ng/mL) compared with those of the rest of the groups, but statistically significant differences were only observed with the miscellaneous and tuberculous groups (P < 0.001). Levels of CRP were also higher in the PAR (0.67 mg/L) compared with those of the rest of the groups, with statistically significant differences observed (P < 0.001-0.004) in all of them. The parameter with the largest area under the receiver operator characteristics curve was the product of the total neutrophil count and the CRP in the pleural fluid, in which an area of 0.836 had a sensitivity of 64.3% and a specificity of 93.4%.

Conclusions: Determination of procalcitonin and CRP, in the pleural fluid and blood, does not seem to provide great value to the diagnosis of PAR. However, calculating the product of the total neutrophil count and the CRP may be useful in the diagnosis of these effusions because increased values have a high specificity and predictive values.