Age : pleural fluid ADA ratio and other indicators for differentiating between tubercular and malignant pleural effusions.

Most of pleural effusions are caused by tuberculosis and malignant tumor. Difficult sampling and bacterial sparing nature of these diseases challenge doctors' diagnosis in China. This study aimed to develop a new convenient and effective method for the differentiation of tuberculous and malignant pleural effusion. A prospective cohort study of patients hospitalized with malignant (n = 90) and tuberculous (n = 130) pleural effusions from September 2018 to October 2020 was performed. The diagnostic performance of the age to pleural fluid ADA ratio (age/ADA) and other indicators to distinguish tuberculous and malignant pleural effusions was evaluated by receiver operating characteristic (ROC) curve analysis. The areas under the curve (AUC) of age/ADA and pleural fluid ADA were largest. Age/ADA showed sensitivity and specificity of 81.5% (95%CI 73.8%-87.8%) and 97.8% (95%CI 92.2%-99.7%) respectively. The sensitivity and specificity of pleural fluid ADA were 83.1% (95%CI 75.5%-89.1%) and 93.3% (95%CI 86.1%-97.5%) respectively. The positive likelihood [36.69 (95%CI 9.3-144.8)] of age/ADA was significantly higher than that of pleural fluid ADA [12.46 (95%CI 5.7-27.1)]. The AUCs for Cancer Ratio and Cancer Ratio plus were lower and showed a sensitivity of 80.0% (95%CI 72.1%-86.5%), 80.0% (95%CI 70.2%-87.7%) and a specificity of 81.5% (95%CI 73.8%-87.8%), 80.0% (95%CI 70.2%-87.7%) respectively. Age/ADA has a higher diagnostic accuracy than ADA. Age/ADA is a promising diagnostic index for tuberculous and malignant pleural effusion with high sensitivity and specificity, especially the high positive likelihood ratio. The diagnostic accuracy of Cancer Ratio and Cancer Ratio plus are inferior to those of age/ADA and ADA.