You probably know that hospital bills can be shockingly high. But did you know that they frequently harbor errors? And not just a misspelling of your name, either. Pay close attention to your next hospital bill and you may well save yourself from forking over a lot of money erroneously.

A article on the topic cited one hospital bill auditor, Nora Johnson, who said that, "More than 90% of the hospital bills I've audited have gross overcharges." It also notes that, "Estimates on hospital overcharges run up to $10 billion a year, with an average of $1,300 per hospital stay. Other experts say overcharges make up approximately 5% of hospital bills." That's not chicken feed.

Johnson reported that, "I've seen $90 charged for a 70-cent I.V. How about $129 for a mucous recovery system? That's a box of Kleenex."

Here are some common errors found on hospital bills -- courtesy of and Consumer Reports:

  • Getting charged twice for the same procedure, test or products. You may even be charged more than that, if a simple typo has resulted in your being billed for 12 of something which you were only given two of.

  • Being charged for more days than you spent at the hospital. (Hospitals often don't charge for the day on which you leave, so check to see if it's been counted.)

  • Being charged for a more expensive room than you stayed in (such as a private room vs. semi-private).

  • Being charged for a test or procedure that you didn't have.

  • Being charged for medicine you weren't given. This can happen if you're given a generic version of a costly name-brand medication. For example, Fluoxedine is the generic version of Eli Lilly's (NYSE:LLY) Prozac and Cimetidine is the generic version of GlaxoSmithKline's (NYSE:GSK) Tagamet.

  • Being charged for more time than you spent in the operating room. (You might want to station friends or relatives outside the door with stopwatches.)

  • Being charged twice, due to "unbundling" on the bill. For example, if a certain procedure includes five components, your bill might list the cost of the procedure (which includes the components), followed by charges for each of the components.

What else can you do? Request an itemized bill -- otherwise you'll never be able to see exactly what you're being charged for various items. Ask for "simple English" translations of the medical jargon, too. And protect yourself by keeping a log of all your treatments during your hospital stay. If you're too out of it to do so, have a friend or relative keep the log. You'll later be able to compare the log with the bill.

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Longtime Fool contributor Selena Maranjian does not own shares of any companies mentioned in this article.