Whether or not your health insurance will work across state lines comes down to the plan you are carrying. What you're going to be looking for in your policy is the letters "MSP," for Multi-State Plan.
Why Doesn't All Insurance Work In Every State?
Private insurance must contend with the fact that not every company is authorized to operate in every state. In cases of public health care, insurance might not be state agnostic because benefits come from state taxes and are intended to go only to state medical providers for state patients. Healthcare is complicated. With no single, universal federal plan in place, there are simply too many roadblocks for every provider, private or government, to cover their customers in every state.
What Do I Need To Know About MSPs?
A Multi-State Plan gets you a better chance at coverage while traveling through the United States, but it is not necessarily a guarantee that you will be able to get care in any and every part of the country. Many MSPs have state restrictions, while others may rely on a medical provider network with lots of uncovered territory across the country. There may be no restrictions against a Tennessee resident being covered on a trip to Arizona, but if their MSP does not have any health providers in Arizona, then there is no way for the MSP to pay for care in that state.
If you do a lot of traveling, your best bet is to get in touch with health insurance providers offering Multi-State Plans and make sure that they cover your areas of interest before you sign up. Some plans will cover you no matter where you go, but most will not.