BACKGROUND: Soluble intercellular adhesion molecule-1 (sICAM-1), released by endometriotic lesions, is involved in the regulation of cytotoxic processes. Altered levels of sICAM-1 in the circulation could parallel its deregulation in the peritoneal cavity. We therefore investigated whether sICAM-1 could represent a serum marker for endometriosis. METHODS: sICAM-1 levels were measured by enzyme-linked immunosorbent assay in serum samples from 176 subjects with surgically con®rmed endometriosis

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... 34 patients with stage I±II and 42 patients with stage III±IV) and 198 controls with no surgical evidence of the disease. All serum samples were collected during the luteal phase of the menstrual cycle. Detailed information about demographics, symptoms and clinical pro®le were collected. RESULTS: Mean levels of sICAM-1 appeared signi®cantly reduced in patients with stage III±IV endometriosis in a crude comparison of means. However, when means were adjusted for potential confounders such as the pre-operative indication or fertility status, no signi®cant difference between cases with stage III±IV disease and controls was observed. CONCLUSIONS: Serum levels of sICAM-1 during the luteal phase of the cycle are not able to discriminate women suffering from endometriosis from controls when confounders are taken into account. These results underline the importance of careful identi®cation of confounders, based on patients' demographic and clinical data in studies aiming at discovering diagnostic markers for endometriosis.