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

OBJECTIVE: To evaluate CA-125 in peritoneal fluid (PF) as an indicator of endometriosis. DESIGN: 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. PATIENTS: Forty-one women with and without endometriosis, undergoing laparoscopy or laparotomy during the follicular phase of the menstrual cycle, were selected. SETTING: 2nd Institute of Obstetrics and Gynecology, University of Rome "La Sapienza," Rome, Italy. MAIN OUTCOME MEASURE: Peritoneal fluid CA-125 levels obtained using diluted samples were significantly higher than those found using undiluted ones. RESULTS: 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. CONCLUSIONS: 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.