A sudden illness or injury sometimes requires immediate care, and if it's a weekend, evening or your regular doctor isn't available, you might decide to go to the emergency department for treatment. In fact, a study conducted by the National Center for Health Statistics found that about 48 percent of patients who went to the emergency department but were not admitted to the hospital chose the ER because the doctor's office was closed.

This can be costly, since treatment in an can cost two to three times more than the same care in your doctor's office. And since ERs must see the most seriously ill or injured people first, it can be time-consuming as well. Here are a few guidelines that can help you decide where to go when you are sick or injured.

The ER is hospital-based and deals with true emergencies, such as life or limb-threatening injuries or illnesses. Urgent care facilities are same-day clinics that can handle medical problems needing immediate attention but are not considered true emergencies.

Before deciding whether to go to the ER or urgent care ask this question: is the injury or illness something you could talk to your primary doctor about? Your primary doctor is the one who knows that most about you and your medical history and can provide a diagnosis based on not only your current condition but also on your previous medical history. You may also be able to wait for your primary doctor if you have a chronic condition and your symptoms seem familiar.

If the symptoms are ones you don't recognize or are more serious, then urgent care is an option. Urgent care facilities offer walk-in services and can treat a wide range of injuries and illness, such as flu or bronchitis, allergic reactions, cuts and burns, and falls, sprains or broken bones.

Call 911 or go to an ER immediately if you have symptoms such as: loss of consciousness (particularly after a fall or choking), chest pain, suddenly weak or drooping on one side of the body, significant shortness of breath, severe abdominal or back pain, a high fever that won't go away with medicine, heavy bleeding, coughing or throwing up blood, difficulty breathing, an unusual or bad headache (especially if it started suddenly), and/or a seizure that lasts more than three minutes.

When in doubt, of course, come to emergency room, but you can save time and money when you consider these factors as part of your decision-making process.