I worked in the insurance industry for a couple of years. Just about anytime an individual applies for health insurance or life insurance, a background check is done with the MIB. The MIB has records of all previous medical claims. Insurance companies use this to evaluate risk and check on preexisting conditions that were not stated on your insurance application.
If you've been treated for heart conditions or cancer or anything serious, the information is out there and potential insurers can get it.
Then as usual ole Pantie waist gramistey is helping the enemy.
That happened to me when my employer changed insurance. All of a sudden I started receiving weird letters telling me to "check this and this box, sign and return" regarding my visits to a chiropractor.
I took it to my chiropractor, and he told me they had found out that I had been treated for a back injury eight years before. It was a good thing I talked to him about it, because I almost walked right into their little trap.