The concept of an HMO insurance plan involves restricting patients to a specific network of caregivers. Each network recruits many different doctors, specialists and other professionals, and those are presented to the insured person as the options for care. Sometimes, though, the specialist you need to see is not a member of the network you are in. When that happens, your options are limited.
In most HMO plans, visiting a specialist or other physician outside of the network is not allowed. That does not mean that you are prohibited from seeing that specialist, but you may have to pay for the care you receive out of your own pocket. Some plans will pay up to the network agreed price for the care, even outside of the network, but you are still responsible for paying the remainder of the bill, which could be quite a bit more than what your health plan pays.
The best option, if it is available, is to locate a specialist in your network that can provide the same care. Most health plans attempt to foresee the needs of their members and provide member physicians to fill them. In some cases, such as groundbreaking procedures that have not gained mass support yet, this may not be possible, but in most cases you can find a specialist who fills your needs, even though it may not be the physician you would prefer to see.
Finally, if your preferred specialist or doctor is not a member of your HMO, you have the option of asking them to join. Since care givers can belong to more than one HMO network, your chosen specialist may be willing to join and simply has not been asked to do so. In this case, you may be delayed in seeing the specialist until they have joined, but once that has been done you will have the same coverage with them as with any other specialist of the same type who is already in the network. Additionally, you will have introduced a new specialist into the network that other members are able to use as well.