When the history of health care reform is written, it may be insurance companies that get credit for finally closing the deal. That’s because in February, as health reform efforts seemed terminally stalled, policyholders everywhere were learning about rate increases from their providers, usually double-digit percentages. The outrage that spawned helped to build support for Congress to act.

Last week, President Barack Obama hosted executives from a dozen major health insurance companies at the White House. He delivered a stern warning: Don’t use passage of the health care reform bill as an excuse to jack up premiums.

It’s a timely message.

Just a day earlier, the nonpartisan Kaiser Family Foundation had released a survey showing that nationwide, people who buy health insurance for themselves and their families on the so-called individual market faced premium increases averaging 20 percent this year alone.

Insurance companies blame those higher prices on medical inflation. There’s some truth to that. National health spending has increased at about twice the overall rate of inflation in recent years.

But while medical inflation grew by about 40 percent between 2000 and 2008, health insurance premiums grew even faster.

Average premiums for employer-provided family coverage jumped more than 130 percent over the past decade. And that’s for group insurance — the part of the health insurance market that works best. Not only did rates rise, many people who tried to get coverage found it was unavailable at any price.

One of the most surprising findings in the Kaiser study: People who buy health insurance on their own report being somewhat healthier than those who get health benefits through work.

You’d expect just the opposite. People with serious chronic illness are less likely to be able to work full time, and thus are less likely to get health insurance through their jobs like most other Americans.

But unlike with group health insurance policies, people who buy their own coverage can be — and often are — turned down for having a pre-existing condition. Beginning in 2014, under the new health care law, insurers won’t be able to exclude adults with pre-existing conditions. The no-exclusion rules for children with pre-existing conditions go into effect this October.

Until then, however, people who buy insurance on their own and those who work at small businesses are in a uniquely vulnerable position. They deserve special protection. President Obama warned insurance executives that they’ll be asked to justify future rate hikes. It’s a promise he must keep.