NEW YORK (MainStreet) — More than one in four Americans say they are struggling to pay health care costs or can not afford to pay them at all, especially when they are hit with a bill they did not anticipate.

The study from the Centers for Disease Control and Prevention also found that one in five families was paying medical bills over time.

Consumers are often also billed for additional services they did not receive or are not aware that the decisions their health professional made will cost them extra.

One way to prevent any unwanted bills is to know what qualifies as preventive care and what is excluded.

Health care reform has resulted in many preventive care medical services that are free to people who have health insurance. Your annual checkup, immunizations, women's health visits and other services may not cost you a single dime this year, said Carrie McLean, director of customer care at eHealth.com, an online health insurance exchange based in Mountain View, Calif.

"That's great news, but be aware that not all medical care is free," she said. "If your doctor orders lab tests during your next check-up, those tests may not technically qualify as preventive care. You may need to make a copayment for the services or they could apply toward your annual deductible."

Sticking with in-network physicians and hospitals is crucial, especially if you're new to health insurance. Most health insurance plans limit the doctors and hospitals you can use and have a specific network of medical providers that they want you to visit.

"This is part of how they keep costs in check, by negotiating rates with medical provider networks," McLean said.

When you visit a doctor or hospital outside of the network, you may have limited coverage or no coverage at all, depending on the rules for your plan.

"In the end it's up to you to make sure that you're seeing network medical providers," she said. "Even if your primary doctor refers you to a specialist, call your insurance company to make sure that he or she is in the network – it can save you a lot of money."

Being treated by an out-of-network doctor does not necessarily equate to better care, said Robin Gelburd, president of FAIR Health, a New York-based not-for-profit corporation that brings transparency to healthcare costs and health insurance information.

The majority of health insurance plans come with an annual deductible, which is a form of cost-sharing that is similar to co-payments. Medical services such as visits to the doctor when you're feeling ill may apply to your deductible which means you will have to shell out money.

The doctor's office will submit a claim to the insurance company typically and the insurance company will determine the maximum amount that can be paid for that service. If you haven't met your deductible yet, then you may be billed for that service by the doctor. If your deductible is already met for the year, then the insurance company may pay for it on your behalf.

"If you want to avoid nasty surprise medical bills, remember your deductible," McLean said.

If you have health insurance, you probably won't need to negotiate medical costs. However, if you are uninsured or if your plan doesn't cover a specific kind of medical service, it may make sense to negotiate your costs up front. Tell the doctor or hospital that you will be paying for coverage on your own and ask for a discount.

"The fact is that doctors and hospitals are used to discounting the cost of medical care," she said. "They do it all the time for insurance companies. They may be willing to offer you a 10% to 40% discount off the total bill and they could also set up a payment plan for you."

Consumers who are undergoing procedures or surgeries should find out what other doctors besides the primary care doctor will be involved. Specialists such as anesthesiologists and physical therapists could affect the total cost, especially if those specialists are out-of-network, said Gelburd.

"Even if your hospital is in your network, that doesn't mean all the doctors practicing there are, too," she said. "Ask if your surgeon, anesthesiologist, pathologist and lab are in your network. If they are not, ask your primary care doctor to recommend providers who are part of your plan's network."

If an itemized bill is not provided, ask for one to cross-reference against your explanation of benefits. This is crucial if you need a test such as a MRI, PET or CT scan, which might need to be pre-authorized. Many plans will not pay for these services if they are not approved beforehand, she said.

"Make sure to review the charges itemized on your hospital bill, which are often identified by a procedure code for each service and supply," Gelburd said. "Ensure they align with the procedures you discussed with your medical professional. You also may want to compare the charges to typical costs for professional services and supplies in your area using online tools, such as the FAIR Health website at www.fairhealthconsumer.org."

If you do get a surprise bill, don't be afraid to ask your doctor if he or she would be willing to accept a lower rate, Gelburd said. You can also look for a patient advocate group in your community by searching online or asking for a referral from a local hospital or community health center. They may be able to assist you in understanding payment options.

Physicians may suggest health screenings, procedures or prescriptions for a variety of reasons and it's important to find out why, said Michael Mahoney, senior vice president of consumer marketing for GoHealth, a Chicago-based online exchange for health insurance. The rationale behind each part of your treatment is important - especially if it is optional or elective.

"Rising deductibles and narrow networks are incentivizing consumers to take a more active role in deciding how their out of pocket health care dollars are spent or not spent during the course of treatment," he said. "I would encourage everyone to listen to his or her physician's recommendations, but we also need to get the full story. Not taking the time to fully understand your treatment options and making an informed decision might be an expensive mistake whether it's a routine treatment or a major procedure."

-Written by Ellen Chang for MainStreet