Distinguishing Polymorphonuclear Leukocyte-Predominant Tuberculous Pleural Effusion from Parapneumonic Effusion in Patients with Elevated Serum C-Reactive Protein.

Background

Tuberculous pleural effusion (TPE) occasionally presents with polymorphonuclear leukocyte (PMN)-predominant pleural fluid (PF) and elevated serum C-reactive protein (CRP), mimicking parapneumonic effusion (PPE). We investigated factors distinguishing TPE from PPE in this diagnostically challenging setting.

Methods

We retrospectively reviewed consecutive patients with confirmed TPE or PPE at a tertiary referral center (2010-2024). Patients with serum CRP ≥ 10 mg/dL were classified according to PF PMN-predominance. Independent discriminators between PMN-predominant TPE and PPE were identified using multivariable Firth logistic regression.

Results

Among 414 patients with confirmed TPE, 108 (26%) had serum CRP ≥ 10 mg/dL, including 20 with PMN-predominance and 88 without. Anti-tuberculosis treatment was modestly delayed in the PMN-predominant group (p = 0.017). These 20 patients were compared with 335 PPE patients showing the same CRP/PMN profile. Pulmonary nodular lesions on chest computed tomography and PF adenosine deaminase (ADA) were independent discriminators. A composite two-tier rule-nodular lesions present or PF ADA > 80 IU/L if absent-achieved an AUROC of 0.925, 80.0% sensitivity, and 86.2% specificity.

Conclusions

In patients with PMN-predominant pleural effusion and elevated serum CRP, this simple, readily available rule may help identify patients warranting early pleural biopsy and heightened suspicion for TPE before microbiological confirmation.