For a small, self-selected group of Americans, cost-sharing ministries make our broken health care system bearable. There is much to admire in their nonprofit structure and their tireless advocacy for members. The problem is that too often their proponents take them as proof that it’s “in the DNA of Americans to assist and help one another” and success comes “when the marketplace is given the opportunity to produce solutions on its own,” as Dale Bellis, Liberty HealthShare’s executive director, put it.

When Theresa Bixby, 63, learned that she had breast cancer four years ago, she reacted as many Americans do. “One of my first thoughts was, ‘will they pay?’ ” she said. But she wasn’t talking about a conventional insurance plan. She lost hers when she left her full-time position for part-time work at her church in Greenville, S.C. She was worried about the program that she had joined six months earlier: Christian Healthcare Ministries.

Christian Healthcare Ministries is not an insurance company. It is a nonprofit “health care sharing ministry” based in Barberton, Ohio. The cost of membership is far lower than the rates of traditional insurance policies — $45 a month for the cheapest plan — but the ministry makes no guarantees of payment. Members send their monthly “gift” to an escrow account, which disburses payments for eligible medical bills, excluding costs like routine physicals, continuing treatment for pre-existing conditions or procedures that members have voted to exclude, like care for pregnancies outside wedlock.

Each time Ms. Bixby visited her hospital for tests or chemotherapy, she explained that she was a self-pay patient and a member of a cost-sharing ministry. Sometimes the receptionist nodded; sometimes she got a blank stare. The hospital never denied her treatment, but “I was getting a two-inch stack of bills every month, and threats that they would take me to collections,” she told me.

Christian Healthcare Ministries assigned her case to a “member advocate,” who negotiated discounts on her fees. These counted toward Ms. Bixby’s $5,000 deductible, so she paid out of pocket only for office visits. In the end, the ministry persuaded the hospital to lop $220,900 off a bill of $301,540 and reimbursed or paid directly the remaining $80,640.

Despite stories like this, organizations such as Christian Healthcare Ministries claim a modest membership. The four main cost-sharing ministries in the United States have about 340,000 members. Regulators in several states have raised concerns that these ministries offer the illusion of insurance while sidestepping the Affordable Care Act’s baseline standards of coverage and skirting requirements that apply to conventional insurance companies, like minimum cash reserves. Nonetheless, membership in the ministries has been growing, particularly since the act granted them an exemption as one of the only ways to avoid the law’s mandate to buy insurance without paying a fine.

But the debate over consumer protections may disguise a more interesting question: Could this model scale up? These ministries seem to achieve a remarkable level of member satisfaction, even if they sometimes must portion out reimbursements when the bills outstrip monthly contributions.

The ministries’ appeal lies partly in their low fees, but also in their ideological boundaries. “This isn’t something that’s for everyone,” said Tony Meggs, the C.E.O. of the Florida-based Christian Care Ministry, which runs a health care sharing program called Medi-Share.

Christian cost-sharing ministries have been around for about 30 years. They claim that their true origins lie in the Book of Acts, the biblical account of how the first Christians “had everything in common” and “gave to anyone as he had need.” The ministries “show the world something that works, and works well, and is a reflection of the commandments of Christ,” Mr. Meggs said.

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