CLEVELAND -- Medical bills are not only tough to pay, but they can be almost impossible to decipher. The procedures, the codes, the unit costs -- it's all difficult for the average patient to understand.

But that's what faced self-employed landscaper Steven O'Shea two years ago when he had an accident while trimming a tree

"I slipped and I fell. I fell into the chainsaw as it was cutting and it cut halfway through my left arm," O'Shea said.

Doctors were able to repair O'Shea's arm but the injury to his bank account was devastating. He had no insurance and the bill was $39,000. He called the hospital billing office asking for help

O'Shea said, "She basically said, 'It is what it is and either you pay it or we'll come after you with bill collectors and put a lien on your house if we have to.' "

O'Shea's wife went to the internet searching for solutions and found a web site for Medical Billing Advocates of America. Their members are trained to help consumers fight unfair or incorrect hospital bills.

"I do a review. I revise, re-price and resolve their hospital and medical bills for them," medical billing advocate Steve Kay said.

For the uninsured there are often two big issues: higher than average charges and mistakes.

Kay said, "According to a Harvard study 90 percent of all hospital bills contain errors."

And in bills that are often hundreds of pages long, the errors can be significant.

"Real serious money ... thousands of dollars," Kay explained.

Medical bill advocates get a detailed copy of your bill and go over it line-by-line. They check procedure codes. And with thousands of them, it's easy to see how a transcribed number could make it onto a bill.

Some mistakes, however, are obvious -- like the bill sent to a patient who passed away in August.

"(They) got a bill two weeks later for services rendered for $2,400 after he was deceased," Kay said.

But for the increasing number of patients without insurance, perhaps a bigger problem is the fact that individuals are charged more than insurance companies for the same services.

Kay said, "It's probably in the neighborhood of about 70 percent."

In O'Shea's case, his medical bill advocate, Nora Johnson, found more than $11,000 in mistakes.

"They were charging me, I think, twice for a nerve repair," O'Shea said.

Then she negotiated a 75 percent discount to get his bill closer to what an insurance company would have to pay.

O'Shea said he ended up paying a little more than $6,000.

O'Shea was happy to pay the adjusted bill. He said his doctors did a great job saving his arm and his medical billing advocate did a great job saving his house and bank account.

"If it hadn't been for her, I don't know where I'd be right now. I'd be in debt," O'Shea said.