Kidney infection, also known as renal infection or pyelonephritis, happens when bacteria from the urinary tract travel up the urethra and affect one or both kidneys.

Most of the time, the bacteria that cause kidney infections come from another part of the urinary tract, such as the bladder, ureters, or urethra.

Kidney infections most commonly affect people who already have a bladder infection, females, and pregnant people.

People who experience the symptoms of a kidney infection should seek medical attention as soon as possible, as the condition may cause permanent kidney damage or spread to other parts of the body.

This article will explain the symptoms of a kidney infection and how doctors diagnose and treat it.

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

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People usually develop kidney infections quickly, within a day or a few hours. Kidney infection symptoms include:

If there is a corresponding urinary tract infection (UTI), the individual may experience pain or difficulty while urinating. This may feel like a burning or stinging sensation. Other symptoms can include:

Males and females will have similar symptoms if they have a kidney infection.

Females are more likely to contract a kidney infection. A female’s urethra is typically shorter than that of a male. A female’s vagina and anus are also closer to the urethra. This can make it easier for bacteria to enter the body via the urinary tract. Pregnant females are also more likely to develop a UTI or kidney infection.

A male under 65 years of age presenting with a UTI is likely to have the possibility of other conditions ruled out first. Doctors may check the person for other types of infection and for signs of a UTI.

Learn more about UTIs in males here.

A kidney infection happens due to bacteria or viruses entering the urethra and reproducing in the bladder, triggering an infection. Most of the time, a kidney infection is the result of a bladder infection that travels to the kidneys.

An infection may happen because of:

  • transference from bowel to genitals during sexual intercourse
  • accidentally transferring feces to the urethra while wiping with toilet paper after a bowel movement
  • contracting a UTI

Risk factors of kidney infection include:

What is the urinary tract?

The urinary tract consists of:

  • Kidneys: The majority of humans have two kidneys, one on either side of the abdomen. Kidneys remove poisonous substances from the blood.
  • Ureters: Urine passes from the kidneys to the bladder through tubes called ureters. Each kidney has one ureter connecting it to the bladder.
  • Bladder: This is a hollow organ in the lower abdomen that stores urine.
  • Urethra: A tube that carries urine from the bladder to outside the body. In males, the urethra travels down the middle of the penis to an opening at the end. In females, the urethra runs from the bladder to just above the vaginal opening. The urethra in females is shorter than in males.

Learn about what urologists do here.

A person with a suspected kidney infection will have their urine tested. The usual course of treatment for a kidney infection is antibiotics, though some people require other forms of treatment.

Antibiotics

If a person’s symptoms suggest an infection, a healthcare professional will prescribe antibiotics before the test results return. A person may also take pain relief.

When taking antibiotics, a person must finish the whole course of medicine. When test results return, a medical professional may change the antibiotic to one that will more effectively treat the infection.

Types of antibiotics

The antibiotics prescribed depend on the person presenting with the infection and their medical history. Some people may have a sensitivity to certain antibiotics. The first treatment usually involves a general antibiotic, with stronger medication available if the first one fails. Antibiotics for the treatment of a kidney infection include:

Fluids

A person with a kidney infection should consume plenty of fluids to help prevent fever and dehydration. Fluid intake recommendations may vary, depending on the type of infection.

Hospital treatment

A person whose symptoms are not improving or who has more severe symptoms may require treatment in hospital. A person may have antibiotics administered intravenously through a vein in their arm.

If a person experiences dehydration, they may have fluids administered with a drip. Most cases of hospitalization do not last more than 3–7 days.

Surgery

A person who has a kidney stone or enlarged prostate that is blocking their urinary tract may require treatment through surgery.

A medical professional will usually check a person’s medical history for health conditions that link to a kidney infection. Diagnostic procedures may include:

  • Physical examination: A medical professional will carry out a physical examination, checking a person’s general state of health, including heart rate, blood pressure, temperature, signs of dehydration, and respiratory rate. A healthcare professional will assess the mid to lower back for pain, sensitivity, or tenderness.
  • Rectal examination: If a person is male, a medical professional may check for an enlarged prostate blocking the neck of the bladder using a digital rectal examination.
  • Pelvic examination: If the person is a young female, the doctor may carry out a pelvic examination to verify whether there is any asymptomatic pelvic inflammatory disease. A female may also need to take a pregnancy test.
  • Urine sample: A person will collect a mid-stream urine sample in a special container for lab analysis. If the urine sample contains bacteria and white blood cells, it could indicate an infection. Both symptoms and lab results can help diagnosis.
  • Imaging: A healthcare professional may ask for imaging of the kidney area, including a CT scan, MRI scan, or ultrasound.

If a person does not seek prompt treatment for a kidney infection, there is a risk of serious complications, including:

  • Emphysematous pyelonephritis (EPN): This is a very rare, potentially fatal complication. EPN is a severe infection in which necrotizing bacteria destroy kidney tissue. Symptoms include fever, nausea, abdominal pain, vomiting, and confusion. Risk factors include women living with diabetes. A person may require surgery if they have this condition.
  • Kidney abscesses: Pus can accumulate in kidney tissues in abscesses. Symptoms include blood in urine, weight loss, and abdominal pain. Sometimes surgery is necessary to drain the pus. Risk factors include kidney stones, pregnancy, and diabetes.
  • Acute renal failure: One or both kidneys may stop working. A person may need dialysis while treatment starts to take effect.
  • Renal vein thrombosis: A blood clot in one of the major kidney veins may result in a lack of blood to the organ. This condition can cause acute kidney injury or chronic kidney disease.
  • Blood poisoning, or sepsis: Sepsis is a medical emergency that needs swift medical diagnosis and treatment. It results in a person’s blood pressure dropping very low, affecting blood circulation. Blood can be moving so slowly that it begins to clot within the blood vessels. The kidneys can begin to fail if the blood is not circulating correctly. Symptoms of sepsis include:

Learn more about sepsis here.

Risks of complication

Anyone who suspects they have a kidney infection should seek prompt medical attention. Kidney infections may be especially likely to cause complications in:

  • males
  • pregnant females who may have asymptomatic infections
  • people with an obstruction in the tubes from the kidneys
  • immunocompromised people
  • adults over 80 years old
  • hydronephrosis, or swelling of one or both kidneys as a result of a blockage in the ureter or an anatomical abnormality
  • kidney stones, or renal tract calculi
  • a rare, abnormal connection between the bladder and the colon or colovesical fistula
  • a person who has had a catheter inserted, or as a result of relying on a catheter after medical procedures
  • infections that occur or persist despite good treatment

If a person does not seek medical advice, they could develop serious complications.

Contact a medical professional if a person is:

  • experiencing persistent pain in the mid to low back or side
  • feeling shivery or has a fever
  • experiencing nausea or generally feeling unwell

Often, a kidney infection is the result of a preexisting infection in the urinary tract. The best way to help prevent a kidney infection is by taking steps to help avoid an infection in the urethra or bladder. Some tips around factors that can help prevent a kidney infection include the following:

  • Hydration: Drink plenty of fluids, particularly water.
  • Urination: Urinate whenever there is an urge. Do not wait.
  • Sexual intercourse: Urinate after sexual intercourse. Wash the genitals before and after intercourse.
  • Hygiene: Wash the genitals every day. Do not use deodorant sprays or a douche on the genitals.
  • Toilet hygiene: After passing stools, wipe the anus from front to back. This reduces the risk of spreading bacteria to the genitals.
  • Fiber: Eat plenty of fiber so that stools come out easily and do not cause irritation or skin lesions. Constipation increases the risk of developing a kidney infection, and a lack of fiber has links with kidney stones.

A kidney infection can be the result of a number of conditions, the most common of which is a UTI. Females of all ages and males over 65 years are more likely to contract a kidney infection. Most kidney infections will resolve themselves with plenty of fluids, preferably water, and a short course of antibiotics. Some people may require additional treatment.

A person should consult with a medical professional if they suspect a kidney infection. Some infections can lead to more serious conditions that may require hospital treatment.

A person can reduce their chances of contracting a kidney infection through:

  • maintaining good hygiene and good toilet habits after passing stools
  • wiping front to back after passing stools
  • urinating and washing the genitals after sexual intercourse