Diagnostic value of pleural fluid carbohydrate antigen 242 for malignant pleural effusion.

Background: Carbohydrate antigen 242 (CA242) shows potential as a tumor marker in the diagnosis of malignant pleural effusion (MPE). However, previous studies have been limited by small sample sizes and a narrow range of etiological types. Therefore, this study aims to reevaluate the diagnostic value of CA242 for MPE by expanding the sample size, encompassing diverse etiologies, and employing electrochemiluminescence immunoassay combined with receiver operating characteristic (ROC) curve analysis and decision curve analysis (DCA). Methods: We prospectively recruited patients with undiagnosed pleural effusions from Hohhot, China, and measured pleural fluid CA242 concentrations using electrochemiluminescence. The diagnostic accuracy and net clinical benefit of pleural fluid CA242 for identifying MPE were assessed using ROC and DCA. Results: A total of 153 patients were enrolled, comprising 66 with MPE and 87 with benign pleural effusion (BPE). The CA242 level in the pleural fluid was significantly higher in patients with MPE than in those with BPE. The area under the ROC curve (AUC) for pleural fluid CA242 as a tumor marker for diagnosing MPE was 0.71. At an optimal cut-off value of 11.46 U/mL, pleural fluid CA242 demonstrated a sensitivity of 0.67 [95% confidence interval (CI): 0.55-0.77] and a specificity of 0.68 (95% CI: 0.57-0.77). The decision curve for pleural fluid CA242 as a tumor marker for diagnosing MPE was consistently above the reference line. Notably, when pleural fluid CA242 levels exceeded 20 U/mL, the specificity for diagnosing MPE reached 100%. Conclusions: Pleural fluid CA242 has moderate diagnostic performance for the identification of MPE.