Even when they can cite prices, going rates for the procedure may vary from hospital to hospital by a factor of 10, researchers found.
"It was very frustrating," said Jaime Rosenthal, a student at Washington University in St. Louis, who led the new research.
"You got transferred to all these different people. You had to leave messages, call back."
According to the U.S. Centers for Disease Control and Prevention, about 327,000 Americans had a hip replaced in 2009.
The surgery is especially common among the elderly, who are covered by Medicare. Still, about half of all hip replacements in the U.S. are done on people younger than 65 - some of whom may not have private insurance.
For the new study, Rosenthal called 122 hospitals: two per state and two in Washington, D.C., plus the top 20 orthopedic hospitals listed in the US News and World Report rankings. During each call, she pretended to have a 62-year-old grandmother who needed a hip replaced but didn't have insurance, and asked for the total price of the procedure.
Just 45 percent of the top 20 hospitals and 10 percent of other hospitals could provide a complete cost for the hospital and doctor fees for a hip replacement, after up to five phone calls.
When Rosenthal called both the hospital and affiliated
Those totals ranged anywhere from $11,100 to $125,798, Rosenthal and her colleagues from the University of Iowa reported Monday in JAMA Internal Medicine.
She said some hospitals gave her reasons for a higher price - such as assigning her grandmother to a private room - but for others, it wasn't clear what went into the cost of care.
"It just points to the fact that most of us in the health system don't have any idea what the costs really are," said medical ethicist Dr. Ezekiel Emanuel from the Perelman School of Medicine at the University of Pennsylvania in Philadelphia, who co-wrote a commentary published with the new study.
Often, only the hospital's billing office knows how much a patient is actually charged for a procedure such as a hip replacement, researchers noted.
Some of the variation in costs has to do with how hospitals factor in overhead to each patient's bill, Emanuel told Reuters Health. And the cost of an actual hip prosthesis can vary four- or five-fold across the country, he added.
Jeanne Pinder, founder of the transparency group ClearHealthCosts, said a ten-fold difference in price for any given test or procedure isn't unusual, even within a single geographic area.
"Nobody has any idea what they will pay in healthcare because the marketplace is completely opaque," Pinder, who wasn't involved in the new study, told Reuters Health.
"When you go into the system, you're usually not there because you want to be. You're usually anxious, upset, and there's a question of when you come out on the back end, whether you'll be bankrupt or not."
That's not only a concern for uninsured people, she noted, given how high co-pays or deductibles may be for those who are covered.
For a patient looking for cost information, there aren't a lot of options right now - other than waiting for more transparency to come through legislation or other means, researchers said.
"I don't know that the information is readily available right now," Emanuel said. "You can try to call around, especially if it's elective."
Rosenthal told Reuters Health the findings do show that people willing to make lots of calls might have success shopping around for the best deal. But hospitals don't make it easy.
"Patients can take responsibility and put pressure on hospitals to make this information available," she said.
Pinder agreed. "I always recommend that people ask," she said. "If you put this information into people's hands… you can start to think like a consumer."