Diagnostic accuracy of interleukin-6 levels in peritoneal fluid for detection of endometriosis

To determine, with extended receiver operating characteristic (ROC) curve analysis, the diagnostic value of cytokines showing significantly different peritoneal concentrations between women with and without endometriosis. Multiplex cytokine concentration measurement of IL-2, IL-4, IL-6, IL-10, TNF-alpha and IFN-gamma levels in peritoneal fluid of women with minimal to mild (n = 10) and moderate to severe (n = 26) endometriosis, and 42 controls. Only IL-6 and IL-10 concentrations were significantly higher in endometriosis patients than in controls. Specifically, significantly higher IL-6 and IL-10 levels were found in moderate to severe but not in minimal to mild endometriosis as compared to controls. For evaluation of diagnostic significance, ROC analysis determined discriminating parameters for IL-6, while those calculated for IL-10 were useless. Importantly, ROC analysis for IL-6 levels limited to women with moderate to severe endometriosis showed the highest area under the curve with the sample size sufficient to achieve 90 % power of the test. Finally, extended ROC including cost of analysis for this group of patients determined the optimal cut-off leading to high specificity and positive likelihood ratio resulting in 79 % effectiveness of the test. While our outcomes show moderate usefulness of peritoneal IL-6 levels in discrimination of moderate to severe endometriosis, further studies might be needed to determine the usefulness of peritoneal IL-6 levels in detection of early stages of endometriosis, as such a finding would be more relevant in clinical decision making.