How can insurance companies find out if you have a pre-existing condition??

I have heard people mention the MIB as a source, but where do they get their info? I thought medical records were strictly private, how do they find out your past medical info? Ty!

Insurance companys keep databases of claims experience that they upload to the Medical Information Bureau. So for example, if Anthem has claims experience on you, they upload it to the bureau and United healthcare can then access your claims experience data.

That aside, many times the information gleaned from your first or second claim makes it obvious that you have a prexisting condition. For example, when you fill your first prescription, and it is for an insulin based product - voila - you have diabetes and chances are you weren't just diagnosed. At that point, they go to your physician for additional information (onset of disease, etc), and that is where you get hit with PreEx

Good point...I'll be watching for the answer on this one!!

they check back with other carriers that you had insurance with

Records are private between you and your insuring company and any company you apply for coverage with.
Another way pre-existing conditions are discovered by the insurance company is looking into your medical records after you already have a policy and file a claim.
For example lets say on your application you "forget" to mention you have been suffering from headaches for the last year and have already been to the doctor. You get your new health policy and rush to the Doctor with these headaches and your DR files a claim. The insurance company then request your medical records from the DR and bingo they find you have been seeing this DR for a year with these headaches. In this case the insurance company can rescind your policy and deny all claims. you will be refunded all premiums and you will have to pay your medical bills out of
pocket.
They also consider symptoms that would have caused a reasonable person to seek treatment to be a pre-existing condition. Example, you have a lump on you neck but don't seek treatment until you buy health insurance. When you go to the DR he says when did you notice the lump and you say 6 weeks ago. Bingo pre-existing condition.

Your prescription history is also reported to the MIB.
You can request your MIB below

MIBs get data from insurance companies - both health and life.

When you apply for an insurance policy, you sign a waiver agreeing that the health insurer is permitted to have use of your medical information as it pertains to the policy.

This means that they are entitled to discuss your medical conditions with your doctors, and they also have the right to check your information in the MIB.

If you don't sign the waiver allowing them reasonable access to your medical background, they aren't going to issue a policy.