Some HMO plans offer what's known as a point-of-service (POS) option. This feature allows a member to see physicians and other providers who are not in the HMO's network, and to receive services from specialists without first going through the primary care physician. If the member uses this option, the plan pays a smaller portion of the bill than if the member had followed the normal HMO procedure. The member also pays a higher premium for this option, along with a higher co-payment each time the option is exercised.

The Preferred Provider Organization (PPO) works in the same manner as the HMO with point-of-service option. If a member receives services from a caregiver in the PPO's network, the cost to the member is lower than if he or she had seen a non-network provider. Although they tend to be more expensive than standard HMOs, many people find that the extra flexibility afforded by PPOs in choosing doctors is an important factor to them, and therefore worth the extra cost.

The Provider-Sponsored Organization (PSO) is a group of medical providers (usually made up of doctors, clinics, and a hospital) that circumvent the insurance company middleman and contract directly with patients. As with an HMO, the member pays a premium, along with a co-payment each time a service is used. Within the first six months of enrolling in Medicare, you have an unqualified right to join any Medicare Managed Care plan that operates in the county of your primary residence. In other words, the plan must accept you without any medical screening and on the same terms and conditions as anyone else of your age, regardless of your medical history or physical condition. Additionally, every Medicare Advantage plan must provide at least one month annually of 'open enrollment', which means that during that time anyone who's eligible for Medicare can join the plan regardless of his or her medical history or condition. Many plans designate November as their open-enrollment month, with coverage beginning the following January 1st. Some plans have more than one open-enrollment month per year; others even offer continuous open enrollment.

Like all managed care systems, Medicare Advantage plans can be an economical way to administer health care. But they can also be quite restrictive with regard to the patient's choices concerning his or her own health care services. If you're considering a Medicare Managed Care plan, you must decide whether any of the offerings available in your area offer coverage that's adequate for you at an affordable cost. For more detailed information about Medicare Advantage healthcare plans, please visit Medicare's website.