The effect of the menstrual cycle on serum CA 125 levels: a population study.

OBJECTIVE: Our objective was to assess the effect of the menstrual cycle on CA 125 levels in a population study. STUDY DESIGN: Serum CA 125 was measured in 1478 women, with day of menstrual cycle noted in 574 women. Repeat examination was performed in women with elevated results, and 40 of these women were tracked by weekly examination of CA 125 levels. RESULTS: A significant difference was demonstrated when midcycle samples were compared with day 1 and day 28 samples (p < 0.05). In spite of this significance the difference was not clinically useful. Elevated serum CA 125 (> 35 U/ml) levels were present in 77 (5.2%) of the premenopausal women. A significant variation was demonstrable with higher CA 125 levels about the time of menstruation in 29 of the 40 women tracked. CONCLUSION: This study suggests that in the population as a whole the effect of the menstrual cycle on serum CA 125 is not clinically significant, but single elevated levels in an individual may represent menstrual fluctuation.