Symptoms of a kidney infection include a dull, aching pain in your back, side, or stomach, urgent and painful urination, fever, and chills. See a doctor if you’re experiencing any of these symptoms.

Urinary tract infections (UTIs) are a very common type of infection, particularly in females. In fact, estimates suggest that between 50 and 60 percent of females will experience a UTI at some point in their lifetime.

Most UTIs affect the urethra or the bladder. However, if the infection spreads to the kidneys, it can become much more serious. In some cases, a kidney infection will require treatment in a hospital.

In this article, we’ll discuss kidney infections in more detail, including the symptoms to look for and when to seek medical care.

Kidney infections are a type of UTI. The medical term for a kidney infection is pyelonephritis. Certain bacteria and viruses can cause these infections.

Experts believe that many kidney infections start as an infection of the lower parts of the urinary tract, such as the bladder or urethra. Many times, these infections happen when bacteria from your bowel enter your urinary tract through your urethra.

It’s possible for a UTI to continue to move up your urinary tract, progressing from your bladder into your kidneys.

Generally speaking, the symptoms of a kidney infection tend to come on over a period of several hours to a day. The symptoms may include:

  • Pain. This is often a dull, aching type of pain that most commonly affects the back, side, or abdomen.
  • Urine changes. If you have a kidney infection, you may notice that your urine is cloudy, smells bad, or contains blood.
  • Urgent, painful urination. A UTI can irritate the lining of your urinary tract. As a result, you may feel the urgent need to urinate and experience a painful, burning sensation when you do so.
  • Fever. People with a kidney infection typically develop a fever, which can often be high. A raised temperature is one of your body’s ways of trying to fight the infection.
  • Chills. Chills are a feeling of being cold without any apparent cause. For example, you could be wrapped up under a blanket and still shiver or feel very cold. In extreme cases, chills may lead to episodes of strong, uncontrollable shaking, which are known as rigors.
  • Nausea or vomiting. The infection may cause you to feel nauseated or to vomit.

It’s important to note that you may not have all of the above symptoms with a kidney infection. If you develop concerning symptoms that may point to a kidney infection, seek prompt medical care.

Kidney infections are serious and require timely care so that they don’t cause complications. According to a 2019 study, estimates suggest that that kidney infections lead to 250,000 office visits and 200,000 hospital admissions in the United States each year.

Deciding where you should go for medical treatment can be confusing, especially when you’re in severe pain. Below, we explain how to know when to see a doctor and when to go to the hospital.

When to make an office appointment

If you have some of the general signs of a UTI, you can schedule a doctor’s appointment to get an evaluation. These symptoms include:

  • urgent, painful urination
  • cloudy, foul-smelling, or bloody urine
  • abdominal pain
  • pelvic or bladder pressure

When to seek urgent care or go to the hospital

Some symptoms point to a more severe infection that needs prompt medical attention.

Go to an urgent care center or hospital if you have any of the symptoms below, which may or may not occur alongside the other UTI symptoms listed above:

  • back or side pain
  • fever
  • chills
  • nausea or vomiting

Kidney infections can cause potentially serious complications. If you feel like something isn’t right, don’t hesitate to seek care as soon as possible.

Without treatment, a kidney infection can cause serious complications. These can include:

Kidney damage

One of the main complications of an untreated kidney infection is kidney damage or scarring. When this happens, your kidneys may not function as well, and you may develop chronic kidney disease.

High blood pressure

Your kidneys work to filter waste products from your blood. If a kidney infection damages the blood vessels supplying the kidneys, this can potentially lead to high blood pressure.

Kidney failure

Serious damage from a kidney infection can cause the kidneys to fail. When this happens, your kidneys are no longer able to filter waste products from your blood.

Kidney abscess

In rare cases, you might develop a kidney abscess, which is a pocket of pus that forms in the tissue of your kidneys.

Sepsis

If the infection moves from your kidneys into your bloodstream, sepsis can occur.

Signs and symptoms of this life-threatening condition include:

  • low blood pressure
  • high fever
  • increased heart rate
  • high respiratory rate
  • laboratory abnormalities

Aggressive treatment is necessary to prevent sepsis from leading to multisystem organ failure and death.

Emphysematous pyelonephritis

Emphysematous pyelonephritis (EPN) is a potentially life threatening condition that happens when the gas that bacteria produce builds up in the kidneys. This rapidly destroys kidney tissue.

EPN tends to be more common in people who have diabetes.

Your symptoms could also result from another common illness. Some similar conditions you may mistake for a kidney infection include:

  • Other UTIs. Other types of UTIs, such as those affecting the urethra and bladder, can also cause symptoms like urgent and painful urination, abdominal pain, and urine that’s cloudy, foul-smelling, or bloody.
  • Kidney stones. Kidney stones are hard deposits of materials like calcium or uric acid that form in the kidneys. When they become lodged in the kidneys, they can cause pain in the abdomen, side, or back, as well as nausea and vomiting.
  • Lower back pain. If low back pain is your primary symptom, you may have a condition that’s affecting your lower back. Examples include injuries, degenerative disc disease, and nerve compression.
  • Pregnancy. Symptoms like frequent urination, nausea and vomiting, and abdominal cramping can all be early signs of pregnancy.

It’s always a good rule of thumb to seek medical attention if you experience any new or concerning symptoms. A healthcare professional can work with you to determine what may be causing them.

Here’s an idea of what you can expect when you seek care for a possible kidney infection.

Tests

A healthcare professional will test your urine to look for signs of an infection. These tests include:

Urinalysis

For this test, a healthcare professional will ask you to urinate into a small container. The sample will go to a lab, where technicians will test for the presence of bacteria, white blood cells, and blood.

Urine culture

If the sample reveals bacteria in your urine, the doctor may choose to culture some of them. Doing this can help them see what type of bacteria is causing the infection, which can guide your treatment.

The turnaround time for a urine culture is typically 24 to 72 hours.

The doctor may also recommend that you undergo imaging to evaluate your kidneys. In this case, they will order an ultrasound or CT scan to help them make a diagnosis.

Treatment

Sometimes, treatment for a kidney infection can happen on an outpatient basis, meaning that you return home afterward.

Treatment for a kidney infection can include:

  • Antibiotics. Antibiotics are medications that can kill bacteria or slow their growth. It’s important to take your entire course of antibiotics, even if you begin to feel better before completing it.
  • Over-the-counter (OTC) medications. OTC medications such as acetaminophen (Tylenol), ibuprofen (Advil, Motrin), and naproxen (Aleve) can help reduce symptoms like pain and fever.
  • Fluids. Drinking plenty of fluids can keep you hydrated and help flush bacteria out of your urinary tract. Aim to drink enough liquid to keep your urine pale yellow.
  • Rest. Resting up as you recover can help your body fight off the infection.

A severe kidney infection will likely need treatment in the hospital. In this case, you’ll typically receive antibiotics and fluid through an intravenous (IV) injection or infusion.

After you’ve recovered from a kidney infection, your doctor may request a follow-up urine culture to make sure your infection has completely cleared.

If the infection is still present, you may need another course of antibiotics to recover fully. However, a 2013 research review notes that experts only recommend this “test of cure” for recurrent or complicated infections.

With timely antibiotic treatment with antibiotics, the outlook for people with a kidney infection is good.

However, certain factors increase the risk of serious illness or complications. People at higher risk include:

Kidney infections can happen when bacteria enter your urinary tract and travel to your kidneys. This condition is serious and requires prompt medical attention.

If you develop symptoms of a kidney infection, go to an urgent care center or a hospital as soon as you can. While many kidney infections are very treatable with antibiotics, serious complications can happen if there’s a delay in treatment.