Pleural fluid C-reactive protein contributes to the diagnosis and assessment of severity of parapneumonic effusions

Diagnosis of pleural infection: state-of-the-art

“…The latter is an acute phase reactant commonly used as an infection marker. It was found that pleural fluid CRP greater than 100 mg/L (sensitivity 36%, specificity 98%, LR 19.4) and a percentage of neutrophils above 85% (sensitivity 44%, specificity 94%, LR 7.8) were the most important parameters in the identification of parapneumonic effusions, both exhibiting areas under the curve (AUC) higher than 0.80 [22].…”

“…Recently, it has been shown that CRP levels higher than 100 mg/L in the pleural fluid were an equally effective marker of complicated parapneumonic effusions (sensitivity 58%, specificity 88%, LR 5) [22]. The combination of CRP with either pH or glucose at the established cutoff points using an "or" rule, wherein the pleural space would be drained if any test is positive, increased sensitivity for detecting complicated parapaneumonics to nearly 80% [22].…”

“…The rationale behind this is that the more advanced the pleural space infection is, the lower the pleural fluid pH and glucose levels become. If the pleural fluid pH is less than 7.20 or the pleural fluid glucose is below 60 mg/dL the pleural space should probably be drained (LR about 5.5) [22,23]. Nevertheless, about 40% of patients who will eventually be treated by tube thoracostomy have values above these thresholds [22].…”

“…The combination of CRP with either pH or glucose at the established cutoff points using an "or" rule, wherein the pleural space would be drained if any test is positive, increased sensitivity for detecting complicated parapaneumonics to nearly 80% [22]. On the other hand, the presence of both high CRP and low pH or glucose values argues strongly for pleural fluid drainage (specificity 97%, LR 15) [22]. The theoretic advantage of combining several biomarkers into a single classification rule is that it should help to improve their classification accuracy and, therefore, their clinical usefulness.…”

“…However, a pleural fluid dominated by polymorphonuclear leukocytes can also occur in 10% and 20% of tuberculous and malignant effusions, respectively, as well as in a number of acute effusions [21]. Recently, Porcel et al examined the diagnostic usefulness of pleural fluid routine biochemistries (white blood cell count and differential, pH, glucose, lactate dehydrogenase [LDH], adenosine deaminase [ADA]) and C-reactive protein (CRP) for labeling parapneumonic effusions among nearly 2,000 non-purulent exudates [22]. The latter is an acute phase reactant commonly used as an infection marker.…”