Hospitals are required by federal law to publish what they charge — every CPT code, every insurance plan, the dollar amount. The bill in your mailbox has to line up with that file. When it doesn't, you can fight it.
Three patterns account for almost every disputable charge:
A service billed twice. A service you didn't receive. A line item for "supplies" that doesn't match anything that happened in the room.
A radiologist or anesthesiologist quietly billed at non-contracted rates inside an in-network procedure. Your insurer pays partial; you get the balance.
A more expensive CPT billed for the procedure you actually had. A 99214 billed for a visit that was clinically a 99213. The hospital's own MRF tells you the price difference.
One you do yourself for free. One a service does for a percentage of what they save you. Pick by how much time you have.
Pull the hospital's MRF (linked from every hospital row on Itemized). Find your CPT codes. Compare line by line against your itemized bill. Write a dispute letter citing the published rate. Hospitals know they have to honor what they published.
Bill negotiation services review your itemized bill, find the disputable charges, and negotiate with the hospital on your behalf. They take a percentage of what they save you. If they don't save anything, you don't pay.