What is an HMO?

A health maintenance organization ( HMO) is a type of managed care organization (MCO) that provides a form of health care coverage in the United States that is fulfilled through hospitals, doctors, and other providers with which the HMO has a contract. The Health Maintenance Organization Act of 1973 required employers with 25 or more employees to offer federally certified HMO options. Unlike traditional indemnity insurance, an HMO covers only care rendered by those doctors and other professionals who have agreed to treat patients in accordance with the HMO's guidelines and restrictions in exchange for a steady stream of customers.

Most HMOs require members to select a primary care physician (PCP), a doctor who acts as a "gatekeeper" to limit access to medical services. PCPs are usually internists, pediatricians, family doctors, or general practitioners (GPs). Absent a medical emergency, patients need a referral from the PCP in order to see a specialist or other doctor, and the gatekeeper cannot authorize that referral unless the HMO guidelines deem it necessary.

"Open access" HMOs do not use gatekeepers - there is no requirement to obtain a referral before seeing a specialist. The beneficiary cost sharing (e.g., co-payment or coinsurance) may be higher for specialist care, however.

HMOs also manage care through utilization review. That means they monitor doctors to see if they are performing more services for their patients than other doctors, or fewer. HMOs often provide preventive care for a lower copayment or for free, in order to keep members from developing a preventable condition that would require a great deal of medical services. When HMOs were coming into existence, indemnity plans often did not cover preventive services, such as immunizations, well-baby checkups, mammograms, or physicals. It is this inclusion of services intended to maintain a member's health that gave the HMO its name. Some services, such as outpatient mental health care, are limited, and more costly forms of care, diagnosis, or treatment may not be covered. Experimental treatments and elective services that are not medically necessary (such as elective plastic surgery) are almost never covered.

Other Choices for managing care are case management, in which patients with catastrophic cases are identified, or disease management, in which patients with certain chronic diseases like diabetes, asthma, or some forms of cancer are identified. In either case, the HMO takes a greater level of involvement in the patient's care, assigning a case manager to the patient or a group of patients to ensure that no two providers provide overlapping care, and to ensure that the patient is receiving appropriate treatment, so that the condition does not worsen beyond what can be helped.

HMOs often shift some financial risk to providers through a system called capitation. Certain providers (usually PCPs) receive a fixed payment per member per month in exchange for providing certain services, creating an incentive to provide as little care as possible. To counterbalance this trend some plans offer a bonus to providers whose care meets a predetermined level of quality.