Predictive Ability of Sonographic Characteristics Alone to Diagnose Tuberculous Pleural Effusions in a Resource-Limited Setting: A Cross-Sectional Pilot Study in Zambia.

Abstract

Background: Tuberculous pleural effusion (TPE), the second most common form of extra-pulmonary tuberculosis (TB), remains difficult to diagnose due to low-yield, invasive and often unavailable diagnostics in resource-limited settings. This study aimed to evaluate the diagnostic accuracy of sonographic characteristics alone to predict TB aetiology of pleural effusions using point-of-care ultrasound (POCUS).

Methods: This cross-sectional study included 45 participants in Zambia who underwent ultrasound scanning and diagnostic thoracentesis. Key sonographic characteristics of pleural effusions-presence of septations, presence of plankton sign and unilateral location-were evaluated for their association with TB, using pleural fluid adenosine deaminase (ADA) ≥ 40 IU/L, combined with Xpert MTB/RIF and lipoarabinomannan, as the gold standard. Sensitivity, specificity, positive predictive values and negative predictive values were calculated for each characteristic alone and in combination and multivariate logistic regression was used to determine statistical significance. Interrater reliability between clinician and expert image interpretation was calculated using a kappa statistic.

Results: Significant associations were found between TB positivity and unilateral location (either side) (p = 0.037), right-sided location (p = 0.043) and any two POCUS signs (p = 0.044). Diagnostic performance varied across the three POCUS signs, with the presence of any two POCUS signs demonstrating the highest sensitivity (90.9%) but moderate specificity (41.7%) and the presence of all 3 POCUS signs showing strong specificity (83.3%) but poor sensitivity (45.5%). Agreement also varied, with the lowest kappa score observed for the plankton sign and the highest for unilateral location.

Conclusions: Multiple sonographic characteristics, including unilateral location (either side), unilateral right-sided location and any two positive signs were significantly associated with TB aetiology. Limitations included small sample size, potential selection bias, imperfect gold standard options, and inability to fully assess potential confounders. With additional study, these findings may be used to inform development of a non-invasive tool to predict TB aetiology of pleural effusions-and expedite initiation of anti-TB therapy-in high TB settings globally.