Clinical markers of endometriosis: have we been too quick to judge?

Numerous biochemical differences have been documented in women with endometriosis compared to controls; however, identification of a clinically useful marker of endometriosis remains elusive. We postulate that the diversity of clinical presentations, patient objectives, and complexity of the pathophysiology of endometriosis mandates rigorous attention to study design and standardization of procedures and questionnaires that has heretofore been overlooked in the pursuit of clinical markers of this enigmatic disease. We further propose that it is premature to conclude that clinical markers of endometriosis brought forward in the literature lack clinical value in the diagnosis of endometriosis. To address this hypothesis we reviewed the literature and assessed papers according to a modified version of the Quality Assessment of Diagnostic Accuracy Studies (QUADAS) criteria from which 55 high quality papers were reviewed. While pelvic inflammation and pain is a known significant component of endometriosis, control group definitions were widely divergent and included healthy women through to women with other inflammatory conditions. Although pain is a common presenting complaint in women with endometriosis, it was assessed in only 4 of 55 studies (7.3%) whereas infertility was documented in 34/55 studies (61.8%). Disease severity was assessed in 44 of 55 studies (80%) whilst the association between active vs. inactive disease was attempted in only 2 of the studies reviewed (3.6%). We conclude that experimental design criteria are inconsistently applied making comparisons across studies difficult. Thus, the clinical utility of previously described diagnostic markers of endometriosis remains uncertain.