Objectives: Physiological factors are among the preanalytic variables of clinical chemistry laboratory results. One of these factors is the menstruel cycle.

In this study, to reach the most accurate and sensitive results, the probable effects of menstruel cycle on CA 15-3, CA 125 and thyroid hormone (TT3, TT4, FT3, FT4, TSH) levels and their importance were evaluated.

Materials and Methods: Fifteen healthy volunteer women aged between 26-41, who were fertile and had regular menstruel cycles were enrolled to the study. Blood samples were taken during follicular, periovulatory and luteal phases of their menstruel cycles. CA15-3, CA 125, TT3, TT4, FT3, FT4 and TSH levels were determined by immun chemiluminesance method.

Results: CA 15-3 levels in follicular phase were found significantly higher than the levels of those in periovulatory phase (p<0.003). The levels of CA 15-3 in luteal phase were significantly higher than the levels of those in follicular phase (p<0.01). There were no effects of menstruel cycle on the levels of CA 125 and thyroid hormones.

Conclusion: Different phase of menstruel cycle had significant effects on the levels of CA 15-3. However, it seems that menstruel cycle has no effect on thyroid hormone and CA 125 levels. It may be suggested that menstrual cycle must be taken into account when reporhing CA 15-3 levels in among, especially for the levels around upper reference limits.