Apolipoprotein E in patients with undiagnosed pleural effusion: a prospective diagnostic test accuracy study.

Introduction: Pleural effusion is common in clinical practice, and its differential diagnosis remains challenging for clinicians. This study investigates the diagnostic value of apolipoprotein E (apoE) in patients with undetermined pleural effusion.

Methods: This prospective, double-blind study enrolled 152 patients with undiagnosed pleural effusion. Their pleural fluid apoE levels were measured, and a receiver operating characteristics (ROC) curve was used to evaluate the diagnostic accuracy of apoE. Decision curve analysis (DCA) was used to assess apoE's net benefit. Subgroup analyses were performed to investigate the effect of age on the diagnostic accuracy of apoE.

Results: Among the included participants, 23 had heart failure (HF). HF patients had the lowest apoE level among pleural effusion patients. The area under the curve (AUC) of apoE for HF was 0.79 (95% CI: 0.69-0.89). At the threshold of 40 mg/L, the sensitivity and specificity of apoE were 0.96 (95% CI: 0.87-1.00) and 0.33 (95% CI: 0.25-0.42), respectively. The decision curve for apoE was above reference lines. The AUC of apoE decreased in older patients.

Conclusion: Pleural fluid apoE has moderate diagnostic value for HF and has net benefits in patients with undiagnosed pleural effusion. The diagnostic accuracy of apoE decreases with age.