Uh-oh: The House may need to vote on health care (again!)

House Republicans passed the American Health Care Act earlier this month, but there's still a chance they might have to vote on it again before the Senate can take it up.

Republicans are using the budget "reconciliation" process to pass their health care bill, which allows them to push legislation through the Senate with a simple majority. But that depends on the bill meeting certain requirements — and one of them is that it reduces the deficit by at least $2 billion over the next decade.

The trouble is that Republicans voted on their House bill without waiting for the Congressional Budget Office, the federal agency that evaluates legislation, to finish its projections, which are expected next week.

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Bloomberg News reported Thursday and NBC News has confirmed that House leaders have not formally sent their bill to the Senate on the chance that it fails to meet the deficit requirements.

"The bill is just being held until CBO issues its final score," Ashlee Strong, a spokeswoman for Speaker Paul Ryan, said in an email.

A previous version of the American Health Care Act saved $150 billion over 10 years and Republican leaders and some outside health experts believe the new one is likely to maintain sufficient savings. But there were some big changes to the final version that add some uncertainty.

The wildcard is a new provision that would allow states to opt out of Obamacare's requirements that insurance plans carry a minimum package of benefits as well as its rule that insurers charge customers the same price regardless of whether they have a pre-existing condition.

The first version of AHCA saved money in part by insuring 24 million fewer people than current law. If states opt out of Obamacare's requirements, though, millions more might be able to afford cheaper, if less generous, plans. The nonpartisan Committee for a Responsible Federal Budget estimates that if 10 million more people purchased insurance under the new version it would add $300 billion in costs.

If that happens, the House would have to vote again on changes, bringing them back to a politically charged bill that they barely carried over the finish line in a narrow 217-213 vote.