medical debt paid to collections and mortgage loan interest rate.?

You would be incorrect. Once it was turned over to the collection agency, they most likely reported it to one or more of the credit bureaus since it is technically no longer a medical debt and subject to HIPAA. If you are applying for a mortgage, at he least it will affect your interst rate and may even cause a declination.

Yes it will show as paid. Yes, it will have an effect,.

I don't know where you got your "thinking" but it is clearly wrong. When they sent your debt to collections, it became a record on your credit report at the same time. Yes, it will affect the interest rate given on a mortgage. If you have paid off the debt, over time, your credit will improve, and you will get a better interest rate.

Anything that goes to collections can go on your credit report.

You cannot get a mortgage while it is still in collections.

Collections agencies are typically rigorous about reporting. The mere fact that you did not work out a payment plan directly with the hospital & pay as agreed, so that it went to collections is a negative right there. Worse, with collections agency fees, you paid a lot more. That was no longer a "hospital bill" but collections agency - which is what happens to deadbeats.

Expect your mortgage interest rate to skyrocket now, if you can get a mortgage. Has it been at least 3-5 years since the collections account was paid in full?

There are multiple credit formulas. Only one excludes medical debt, one delays it 90 days, but if at a collector it counts. You can get your credit score and copies of your credit reports.

https://www.annualcreditreport.com/index.action

Credit scores at other sites.

Often, you have to wait 7 years for debt to fall off the reports.

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