Serum CA-125 Concentrations DuringMidfollicular Phase, a Clinically Useful and Reproducible Marker in Diagnosis

No noninvasive diagnostic tests reliably discriminate endome-triosis and other pelvic pain-causing diseases. CA-125, originally introduced as a marker for ovarian cancer, is increased by endometriosis, but also by pregnancy and menstruation. Serum concentrations of CA- 125 correlate well with clinical staging and with the clinical course of the disease; they may even have predictive values for pregnancy [1] and may be diagnostically useful [2]. Controversy exists as to the exact timing in the menstrual cycle for CA-l25 to be measured, because CA-125 concentra-tions vary with the phase of the cycle [3]. Measurement during menstruation may enhance the positive predictive value for endometriosis [4]. The ratio of menstrual to follicular (Men/Fol) serum CA-125 assay values has been proposed as a screening test for the early stages of endometriosis [5]. Use of the Men/Fol