Kidney infection

Date Updated: 03/13/2026

Overview

A kidney infection is a type of urinary tract infection, also called a UTI. A kidney infection may begin in the tube that carries urine from the body, called the urethra. Or it may begin in the bladder. The infection can travel to one or both kidneys. The medical term for a kidney infection is pyelonephritis.

A kidney infection needs prompt medical treatment. If not treated, an infection can cause lasting damage to the kidneys. Or the bacteria can spread to the bloodstream and cause a dangerous infection of the blood.

Treating a kidney infection typically includes antibiotics. Antibiotics may be given in the hospital if the infection is severe.

Symptoms

Symptoms of a kidney infection include:

Fever.
Chills.
A burning feeling or pain when urinating.
Having to urinate often.
A strong, lasting urge to urinate.
Back, side or groin pain.
Nausea and vomiting.
Pus or blood in the urine.
Urine that smells bad or is cloudy.
Belly pain.

When to see a doctor

Make an appointment with your healthcare professional right away if you have symptoms of a kidney infection. And if you're being treated for a UTI for more than 2 to 3 days but you're still having symptoms, let your healthcare professional know.

A severe kidney infection can lead to dangerous complications. They include blood poisoning, damage to the body's tissues and, in severe cases, death.

Seek medical care right away if you have a fever, chills, severe pain, bloody urine, or nausea and vomiting. These are signs of a severe infection.

Causes

The most common cause of kidney infections is bacteria entering the urinary tract through the urethra. Once inside, the bacteria can multiply and move up to the kidneys.

Bacteria from an infection in another part of the body also can spread through the bloodstream to the kidneys. And a kidney infection can happen if the flow of urine through the urinary tract is blocked. For example, a kidney stone may block the path of urine and an infection may form. But not all kidney stones cause infections.

Risk factors

Things that increase the risk of a kidney infection include:

Being assigned female at birth. The urethra is shorter in women than in men. That makes it easier for bacteria to travel from outside the body to the bladder. The urethra also is close to the vagina and anus. That also makes it easier for bacteria to enter the bladder. Once in the bladder, an infection can spread to the kidneys. And people who are pregnant are at even higher risk of kidney infection.
Having a urinary tract blockage. Anything that slows the flow of urine can raise the risk of a kidney infection. So can anything that makes it harder to fully empty the bladder. These include a kidney stone, a narrowed urethra or an enlarged prostate gland.
Having a weakened immune system. Medical conditions such as diabetes and HIV can weaken the immune system. Certain medicines also can lower immunity. These include medicines taken after an organ transplant to help prevent rejection.
Having damage to nerves around the bladder. Nerve or spinal cord damage can block the feeling of a bladder infection. That can make it hard to know when an infection travels to a kidney.
Using a urinary catheter. Urinary catheters are tubes used to drain urine from the bladder through the urethra. They also may drain urine directly from the kidneys through an incision in the skin. Catheters are sometimes used after a surgical procedure or diagnostic test. They're also used when people have difficulties getting out of bed or have difficulties emptying their bladders for other reasons.
Having urinary tract stents. Urinary stents are small tubes that are surgically placed in the ureters to help keep them open. These stents may get infected.
Having a condition that causes urine to flow the wrong way. In vesicoureteral reflux, small amounts of urine flow from the bladder back into the tubes that connect the bladder and kidneys. People with this condition are at higher risk of kidney infections when they're kids. And they are at higher risk as adults.

Complications

If not treated, a kidney infection may lead to serious complications. These include:

Kidney scarring. This can lead to chronic kidney disease, high blood pressure and kidney failure.
Blood poisoning. A kidney infection can cause bacteria to spread through the bloodstream. A bloodstream infection is a serious complication of a kidney infection. It may require antibiotics given through a vein in the hospital.
Pregnancy complications. A kidney infection that occurs during pregnancy can increase the risk of having a baby with a low birth weight.

Prevention

You can take steps to prevent urinary tract infections. Doing so may lessen your risk of kidney infection.

Drink fluids, especially water. Fluids help remove bacteria from the body when you urinate.
Urinate as soon as you need to. Don't wait to urinate when you feel the urge.
Empty your bladder after sexual activity. Urinating as soon as possible after sex helps clear bacteria from the urethra. This lowers the risk of infection.
Wipe carefully. Wipe from front to back after urinating and after a bowel movement. This helps prevent bacteria from spreading to the urethra.
Avoid using products in the genital area. Deodorant sprays or other products in the genital area can be irritating.

Diagnosis

To check for a kidney infection, you may be asked for a urine sample. The sample is tested for bacteria, blood or pus. You may have blood in your urine that can only be seen under a microscope.

Your healthcare professional also may take a blood sample for a culture. A culture is a lab test that checks for bacteria or other organisms in your urine and blood.

Other tests may include an ultrasound or a CT scan. And you may have a type of X-ray called a voiding cystourethrography. A voiding cystourethrography uses contrast to take X-rays of the bladder when full and while urinating.

Treatment

Antibiotics for kidney infections

Antibiotics are the first line of treatment for kidney infections. The type of medicine and how long you take it depend on your health and the kind of bacteria found in your urine.

Symptoms of a kidney infection often begin to clear up within a few days of treatment. But you may need to continue antibiotics for a week or longer. Finish taking the full course of antibiotics even if you start feeling better. If you don't take all of the medicine, the kidney infection can come back. Or the infection could get worse and spread to other parts of your body. It could spread to your bloodstream, which can be life-threatening.

Your healthcare professional may want you to have another urine culture test to make sure that the infection has cleared. If the infection is still present, you’ll need to take another course of antibiotics.

Hospitalization for severe kidney infections

If your kidney infection is severe, you may need to be treated in the hospital. Treatment may include antibiotics and fluids through a vein in your arm. How long you stay in the hospital depends on how severe your infection is.

Treatment for recurrent kidney infections

An underlying medical condition such as a misshapen urinary tract can cause repeated kidney infections. If you have repeated kidney infections, you may be referred to a urinary surgeon, called a urologist. If you have a structural issue, you may need surgery to repair it. Rarely, you may be referred to an expert in infectious diseases.

Lifestyle and home remedies

To help you feel better while you recover from a kidney infection:

Apply heat. Place a heating pad on your belly, back or side to ease pain.
Use pain medicine. For fever or discomfort, take a pain reliever such as acetaminophen (Tylenol, others). If you have chronic kidney disease, it's best to avoid or limit use of nonsteroidal anti-inflammatory drugs, called NSAIDs, such as ibuprofen (Advil, Motrin IB, others).
Stay hydrated. Drinking fluids helps flush bacteria from your urinary tract. Avoid coffee, other caffeinated beverages and alcohol until your infection has cleared. They can worsen the feeling of needing to urinate.

Preparing for an appointment

Typically, you see your regular healthcare professional about signs of a kidney infection. If they suspect that an infection has spread to your kidneys, you may need to see a urologist. A urologist is a doctor who treats conditions that affect the urinary tract.

What you can do

When you make the appointment, ask if there's anything you need to do in advance. Ask if you need to change your diet for any tests you may have.

Make note of:

Your symptoms, including any that may seem unrelated to your condition. Also note when they started.
Key personal information, including recent life changes, such as a new sexual partner. Include your past medical history.
The names of all medicines, vitamins and other supplements you take, including doses.
Questions to ask your healthcare professional.

Take a family member or friend along, if possible. They can help you remember everything you talk about with your health professional.

For kidney infection, questions to ask include:

What is the likely cause of my kidney infection?
What tests do I need?
What treatment do I need?
Will there be side effects from treatment?
Do I need to go to a hospital for treatment?
How can I prevent future kidney infections?
I have other health conditions. How can I manage them together?
Are there brochures or other printed material I can have? What websites do you suggest?

Be sure to ask any other questions that you may think of during your appointment.

What to expect from your doctor

Your healthcare professional is likely to ask you questions such as:

What are your symptoms?
How long have you had symptoms?
Do your symptoms come and go?
How bad are your symptoms?
Does anything make you feel better?
What things make your symptoms worse?