Same-day surgery is an outpatient benefit.

Stockbyte/Getty Images

Sometimes a trip to the emergency room can result in a prolonged hospital stay. Treatment of serious injuries and illnesses can involve intensive diagnostic tests, blood transfusions and even surgery. After these treatments, some patients find themselves enduring months of rehabilitation services. When a service requires you to stay in the hospital for more than 24 hours, it is officially categorized as an inpatient benefit.

But not all trips to the doctor's office or even the hospital require you to bring a toothbrush and spend the night. Routine and emergency visits like an annual physical, a broken arm, a set of investigative tests and even some surgeries often take no longer than an afternoon. Any visit that is less than 24 hours is referred to as an outpatient benefit. Outpatients are not required to spend the night in the hospital and are able to come and go on the same day.

Hospitals and treatment facilities provide services for a broad range of conditions, so quite a few benefits fall into the category of inpatient services. In this article, we'll take a close look at the most common inpatient services covered by insurance plans and when these benefits actually kick in. We'll also learn about outpatient benefits, the fastest-growing segment of health care in the United States.

Most policies include a list of hospital services that are covered by a basic plan. These services include what you might expect: room and board for the duration of your stay, general nursing care and diagnostic exams. Generally, oxygen services, the administration of blood and plasma, and use of the operating room and the intensive care unit are covered. Inpatient benefits are the same whether you have an HMO plan or a fee-for-service plan, but in some cases preapproval is required. However, in emergency situations, preauthorization is usually waived.

As with any other benefit, most insurance carriers have specific guidelines for the payment of inpatient services. As mentioned above, most plans require preapproval and often a referral from your primary care physician for a medically necessary treatment. Once you're in the hospital, there is a limit to the number of days within a calendar year that your inpatient benefits will cover. Some plans even include a lifetime limit on inpatient treatment.

In addition to the basic services, most plans have a list of other types of covered inpatient services. To give you a better idea of what is covered when you're stuck in a hospital or other health care facility, we'll discuss the most common inpatient benefits.