Now technically, an insurance company is not supposed to know what is wrong with you. You don't need to call them up and say "I have cancer". I do strong suspect they can tell what is wrong with you by what kinds of tests/procedures/surgeries you have. But its not their business what the results of any of these are. They don't get pathology reports. They just get the bill. They are not supposed to discriminate against you.
However I am sure we have all heard the horror stories of people being dropped by their insurance after a cancer diagnosis, or refusal to renew a policy. I live in Massachusetts which has some very strong consumer protection laws against discrimination due to pre-existing conditions but still, I'm not telling my insurance company anything. They can infer all they want from my multitudinous trips to the doctor but I'm keeping my mouth shut.
Last year, they called me and offered a nurse to help me with any questions I may have. I was a little reluctant to talk to her but did in the end - mostly because I really didn't have any issues to discuss with her. I do know the insurance company has nurses on staff that will answer questions if needed.
This year my insurance company, Blue Cross, announced a new program called 'Blue Health Assessment'. They want me to go online and register and fill in all of my medical information so they can help me manage all my medical issues in one place. No, thanks.
Let me tell you why I am not going to fill this out anytime soon:
1. It would take me days to complete my medical history. I have probably had over 150 doctor visits in the past three years. Plus the previous twenty five years of my life with a few other medical misadventures. I don't have this kind of time.
2. Isn't this like giving secrets to the enemy? I mean they aren't supposed to discriminate and its not their business what is wrong with me so why should I tell them?
3. I'm lazy - see #1.
4. Am I getting paranoid about Big Brother - see #2?
Also, I think I do a pretty good job of keeping track of what is wrong with me myself. I have calendars and spread sheets and can look up and tell you when I had what done when. This is clearly outside my comfort zone so I'm not telling.