Serum and peritoneal fluid CA-125 levels in patients with endometriosis

To evaluate CA-125 in peritoneal fluid (PF) as an indicator of endometriosis. CA-125 levels in paired serum and PF were determined by the one-step immunoradiometric assay. For peritoneal samples, high dilution of the sample (1:100) was used to avoid false low results, caused by the “hook effect” phenomenon. Forty-one women with and without endometriosis, undergoing laparoscopy or laparotomy during the follicular phase of the menstrual cycle, were selected. 2nd Institute of Obstetrics and Gynecology, University of Rome “La Sapienza,” Rome, Italy. Peritoneal fluid CA-125 levels obtained using diluted samples were significantly higher than those found using undiluted ones. CA-125 levels in PF were approximately 100 times higher than those found in paired serum, ranging from 970 to 10,636 U/mL. In patients with endometriosis, CA-125 levels in PF were significantly elevated when compared with the control group. In serum, CA-125 levels increased only in advanced stages of endometriosis. The sensitivity of the CA-125 test for endometriosis in PF is greater than in serum. Therefore, the measurement of CA-125 levels in PF could be useful in the detection of early stage endometriosis, which tends to be overlooked by the CA-125 serum test.