I agree with groundhog - it is an unreliable test unless it is being used to monitor a woman already suffering from a known cancer as a drop in levels in these cases will show that the chemo is being used effectively.
I have found this info
"Is CA 125 testing useful as a cancer screening test?
Although CA 125 is a useful test in monitoring women who are being treated for ovarian cancer, a single CA 125 test is not considered to be a useful screening test for cancer. Some women with ovarian cancer (up to 20%) never have elevated CA 125 levels, while most women who do have elevated CA 125 levels do not have cancer. In fact, because CA 125 can be elevated in so many non-cancerous conditions, only about 3% of women with elevated CA 125 levels have ovarian cancer."
Hope you get some answers soon.
Taz x