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The mistake that's tripling your medical bills

How to save on medical bills

To cut medical bills, consumers should take a leaf from their strategies for other big purchases: Shop around.

Doing so can have a substantial payoff. A Change Healthcare analysis released this spring found that prices can vary by more than 300 percent on the same service, even within a given insurer's network of providers. (See chart below for ranges on some common services.) Sometimes the price gap is even wider.

Another study this year found that giving birth in California might cost as little as $3,000 or as much as $37,000—and that's only for simple vaginal delivery, and after adjusting for factors such as moms who had complications.

Read More What's it cost to have a baby?

Price gaps on medical bills

Service Price range Variance
Colonoscopy$1,379 to $4,242208%
CT scan$307 to $2,747796%
Mammogram$135 to $397195%
MRI scan $511 to $2,815451%
Physical therapy office visit$62 to $228268%
Psychiatrist office visit$55 to $176219%
Tooth extraction$79 to $195147%
Vaginal delivery$4,359 to $12,613189%

Don't think that being insured gives you license to get complacent. With more plans entailing high deductibles and other out-of-pocket costs, big price swings still matter, said Dr. Davis Liu, author of "The Thrifty Patient."

Take that example of giving birth in California. Before factoring in deductibles or copay, a plan that covers 85 percent of the costs of hospitalization—which isn't unusual—might mean new parents are responsible for $450, or up to $5,550.

Check out the video above for tips on getting a better price. Of course, it's not smart to go by price alone. "Make sure you're not compromising on quality of care," said Liu. To do that get details from your doctor about say, what kind of imaging technique is preferable for that MRI, or qualities needed to pick a good physical therapist. Then look at ratings and reviews.

The Leapfrog Group maintains a database of hospital safety scores, while doctor ratings can be found on sites including RateMDs and Healthgrades.

By CNBC's Kelli B. Grant