CALCA and bacterial infectious disease: ROC curve analysis for the ability of PCT, WCC and CRP to predict the presence of concurrent bacterial infection showed an AUC (95% CI) of 0.68 (0.56–0.80), 0.68 (0.55–0.80) and 0.64 (0.50–0.77) respectively (Additional file 5: ROC curve analysis of PCT, WCC and CRP for the ability to predict presence of co-existing bacterial infection in patients presenting with unilateral pleural effusion secondary to malignancy).