Influence of menstrual cycle on serum cholinesterase

This study examined whether the variability in cholinesterase (ChE) values among and within women may be attributed to phase of menstrual cycle and/or circulating progesterone concentration. Blood was drawn from 21 female subjects once a week for 8 weeks and analyzed for ChE activity and for progesterone concentration. Women ranged in age from 25 to 55 years and five used exogenous hormones (oral contraceptives, estrogen supplements, or progesterone therapy); one woman became pregnant during the study. There was a significant positive correlation between serum ChE and progesterone values only for the two women on oral contraceptives although there were large weekly variations within individuals (CV: 4-32%). Age significantly affected ChE values with 36-40 year olds having the lowest values and 30-35 year olds the highest. This variation in serum ChE probably is due to the influence of some sex steroid but, in women, there is not a direct one-to-one relationship between the enzyme and progesterone. However, when interpreting ChE tests used to monitor exposure of women to pesticides age and hormone intake must be considered in order to avoid false positive results.