A cancer patient might live in a town with four oncology groups, but only one accepts his insurance — the one owned by his insurer. A young couple could see huge bills after their child is born, because their insurer agreed to the health system’s rates in exchange for a contract with obstetricians across the country. A woman might have to pay a big sum she can’t afford for basic lab tests at a hospital — inflated rates her insurer accepted so its customers have access to the system’s children’s hospital elsewhere in the state.

And even well-insured patients receive unaffordable bills in this era of high-deductible health plans, narrow insurance networks, and 20% cost sharing.

Health systems, doctor groups, and insurers are merging and coalescing into ever-bigger giants. While these merge

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