When you’re feeling unwell and symptoms are quickly getting worse, you know you need medical attention — but it’s not always possible to get a same-day appointment with your primary care physician.

When sudden and severe sickness requires immediate care, the two most common options are to visit an urgent care or to head to a hospital emergency room — but how do you know which is best?

Fox News Digital spoke with multiple doctors to determine when an urgent care center will suffice and when a trip to the ER is warranted.

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When to go to an urgent care

Urgent care centers provide immediate health care services for walk-in patients, typically offering extended hours and same-day availability.  

They can be considered a “middle ground” between a primary care doctor and the ER, according to Mayo Clinic.

There are 10,728 active urgent care clinics in the U.S. as of earlier this year, according to Definitive Healthcare in Massachusetts.  

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Urgent care centers typically treat a broad spectrum of illnesses and injuries, and may have a treatment or procedure room for performing minor medical procedures such as stitches, casts and low-risk surgery under local anesthetic only, according to the same source.

Other services may include basic laboratory and imaging tests, as well as referrals for additional treatment. 

These centers can be staffed by doctors, nurse practitioners, physician assistants, nurses and other medical professionals.

“If it is after hours or on the weekend, some conditions can accelerate pretty quickly and cannot wait until the next business day,” Mishi Jackson, M.D., lead clinician at Novant Health Union Cross Family Medicine in Winston-Salem, North Carolina, told Fox News Digital. 

“For example, a simple bladder infection can spread to the kidney and bloodstream and cause bad outcomes.” 

“Most patients are pretty good at determining what constitutes something minor versus something major.”

Jackson noted that not all urgent care centers offer the same services. She encourages patients to check in advance to make sure the center they are visiting can help with their needs.

“With minor injuries or illnesses, an urgent care facility may be appropriate,” Matthew Shannon, M.D., director of community emergency medicine at University of Florida Health in Gainesville, Florida, told Fox News Digital. 

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“Most patients are pretty good at determining what constitutes something minor versus something major.”

Below are some of the conditions that can typically be treated at an urgent care, per Mayo Clinic’s website.

When to head to the ER

The ER is open 24/7 and is equipped to treat “life- or limb-threatening health conditions,” Mayo Clinic noted, such as seizure, stroke, severe bleeding, loss of consciousness, heart attack or other escalated medical crises.

The emergency room is equipped with critical care services and personnel that an urgent care clinic doesn’t have, including specialists in cardiology, neurology and orthopedics, according to the same source.

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The ER will also have access to imaging and laboratory equipment that may not be available at an urgent care.

Below are some of the types of conditions that warrant a trip to the ER, as listed on Mayo Clinic’s website.

• Chest pain or pressure
• Compound fracture (bone that protrudes through the skin)
• Head injuries
• Pneumonia
• Seizures
• Severe abdominal pain
• Shortness of breath
• Sudden, severe headache, or paralysis or weakness
• Uncontrolled bleeding

Other emergency conditions include high fever, fainting or sudden onset of symptoms like speech difficulties, confusion or impaired movement on one side of the body, according to Shannon.

A patient who has been involved in a significant motor vehicle crash should also visit the ER.  

Patients may encounter wait times at emergency departments, Shannon noted. 

“All patients who present to emergency departments around the country are triaged according to a system of seriousness of complaints, their medical history and vital signs,” he told Fox News Digital.

“Patients who are identified as ill are brought back quickly, so the medical team can begin their assessment,” he went on. “Trained emergency nursing staff and other providers are assessing you as a patient and administering first-line care.”

“Your care really begins right when you walk in the door and talk to a nurse.”

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If your condition is fairly mild, Shannon recommends trying to see your primary doctor, even if you have to wait a day. 

“If you believe you can wait, it’s certainly reasonable to try to get your primary care to see you,” he said.

“Unfortunately, we don’t seem to have enough primary care providers, and the demand for primary care continues to outstrip supply.” 

When to call 911

If any of the following apply, you should call 911 immediately, according to the American College of Emergency Physicians.

• Your condition is life-threatening and you need immediate medical attention
• You can’t move yourself or another person without causing additional harm
• You aren’t able to drive due to physical or emotional reasons and must be transported to a hospital ER

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Mayo Clinic advises calling 911 “if you are having difficulty breathing, shortness of breath, a life or limb injury, or signs of stroke or heart attack.”