OBJECTIVE: Examine the clinical features of pleural effusions with borderline exudative and transudative properties.

METHODS: Two hundred seven patients who underwent thoracoscopy under local anesthesia between January 2000 and December 2022 were included. We defined pleural effusions that can be defined as exudative by Light?s criteria but are considered transudative by the new criteria proposed by Kummerfeldt et al. (Chest 145:586?592, 2014) as exudative and transudative borderline effusions. The association between the final diagnosis by thoracoscopy and the nature of the pleural effusion was retrospectively investigated.

RESULTS: One hundred twenty-six exudative and 81 cases of exudative/transudative borderline effusions were analyzed. Malignant (62.7%) was the most common diagnosis in exudative effusions, followed by non-specific (16.6%) and tuberculosis (11.9%). In exudative/transudative borderline effusions, non-specific (51.9%) was the most frequent, with malignant (33.3%) and tuberculosis (4.9%) also present. Low pleural fluid pH (cut-off 7.50) was a significant factor in diagnosing malignancy (p = 0.008; sensitivity 69.2%, specificity 55.8%). High pleural fluid ADA (cut-off 24.9 U/L) was crucial for diagnosing tuberculosis (p = 0.02; sensitivity 100%, specificity 80%).

CONCLUSIONS: Malignant disease and tuberculosis are also present in specific percentages of patients with exudative and transudative borderline effusions. Especially in cases of low pleural fluid pH (<7.50) or high pleural fluid ADA (>24.9 U/L), a thoracoscopy should be performed.