Pleural fluid carbohydrate antigen 72-4 and malignant pleural effusion: a diagnostic test accuracy study.

Background: The prognosis of malignant pleural effusion (MPE) is poor. A timely and accurate diagnosis is the prerequisite for managing MPE patients. Carbohydrate antigen 72-4 (CA72-4) is a diagnostic tool for MPE.

Objective: We aimed to evaluate the diagnostic accuracy of pleural fluid CA72-4 for MPE.

Design: A prospective, preregistered, and double-blind diagnostic test accuracy study.

Methods: We prospectively enrolled participants with undiagnosed pleural effusions from two centers in China (Hohhot and Changshu). CA72-4 concentration in pleural fluid was measured by electrochemiluminescence. Its diagnostic accuracy for MPE was evaluated by a receiver operating characteristic (ROC) curve. The net benefit of CA72-4 was determined by a decision curve analysis (DCA).

Results: In all, 153 participants were enrolled in the Hohhot cohort, and 58 were enrolled in the Changshu cohort. In both cohorts, MPE patients had significantly higher CA72-4 levels than benign pleural effusion (BPE) patients. At a cutoff value of 8 U/mL, pleural fluid CA72-4 had a sensitivity, specificity, and area under the ROC curve (AUC) of 0.46, 1.00, and 0.79, respectively, in the Hohhot cohort. In the Changshu cohort, CA72-4 had a sensitivity, specificity, and AUC of 0.27, 0.94, and 0.86, respectively. DCA revealed the relatively high net benefit of CA72-4 determination. In patients with negative cytology, the AUC of CA72-4 was 0.67.

Conclusion: Pleural fluid CA72-4 helps differentiate MPE and BPE in patients with undiagnosed pleural effusions.