Insurance companies often make the initial decision to deny a claim based limited information like a diagnosis or procedure code from a claim form the doctor submits. They rarely see a patient's file for that first decision, said Jennifer Jaff, executive director of Advocacy for Patients with Chronic Illness Inc., a non-profit that helps patients with claim denials.

"When you provide them with additional clinical information … it may turn out to be a very easy decision for them," she said.

- What are the first steps to take after receiving a rejection?

Learn as much as you can about the reason. Get the policy language and any information the insurer used to make its decision. Patients are entitled to this, so persist if the insurer moves slowly.

It's also important to know the insurer's appeal process. This should be laid out in the letter you receive telling you about the rejection. Understand the deadlines for appealing.

"These deadlines are serious," Jaff said. "I've never seen an insurance company grant an extension."

- How do you build your case?

Write a detailed argument with records backing up your claims. Enlist your doctor's help.

If the insurer says it doesn't have to pay because your condition existed before your coverage began, a doctor may be able to argue otherwise.

The insurer may say the treatment isn't medically necessary. Your doctor can illustrate how all alternatives were exhausted before you started receiving the treatment in question.

Rely on more than just a doctor's statement.

"Insurance companies do not assume everything a doctor says in a letter is 100 percent true and accurate," Jaff said. "What they really want to see are the medical records."

Patients should be prepared to send their insurer any of those confidential records that would support their case. If the insurer deems a treatment experimental, some additional research may be needed, and your doctor can help there as well. Medical journal articles can show an insurer that your treatment is a widely accepted practice. If the doctor is unwilling or unavailable for help, Jaff recommends for research the National Institutes of Health website www.pubmed.gov . Patients can use it to search medical journals around the world for articles on their treatment. Abstracts, summaries and some articles are free. Those that are not can be pricey, costing between $30 and $50 to buy online. But patients also can check with a medical library near them for copies.

Asking for a compassionate allowance may be another strategy for patients. Some insurance policies will make exceptions to cover something they normally wouldn't cover if it is deemed lifesaving.

An employer that offers a self-funded plan also might be persuaded to overrule the insurer and permit coverage, but Jaff said this is rare. Self-funded plans are generally used by big employers. In those cases, they provide the actual insurance and the managed care company just administers the plan.

Ask your human resources department if your company plan is self-funded.

- What are the keys to a successful appeal?

Keep your emotions out of the argument and give the insurer something new to consider. Avoid rehash information the company already has.

"It's a business decision, it's not personal on the insurer's side," said Pat Jolley of the Patient Advocate Foundation, another non-profit that helps people handle payment problems.

Know your insurer's appeal process. Some may offer a couple rounds of internal reviews and provide a specialist to examine your claim. That means you can have an oncologist review your claim for cancer treatment.

Keep detailed notes of your contact with the insurer, including which representative you spoke to and when.

Send appeals by certified mail to document when an insurer receives them in case the company later claims you missed a deadline.

Communicate in writing whenever possible. This keeps you from having multiple phone conversations with different insurance representatives who provide different answers.

Be persistent. You may have to go through a few rounds of appeals and then take your case to an external review that involves a third party. The process varies by state and insurer.