Pyelonephritis (Kidney Infection) Causes, Symptoms, Diagnosis, Treatment, Prevention

Pyelonephritis (Kidney Infection) Causes, Symptoms, Diagnosis, Treatment, Prevention

What is a  Pyelonephritis (Kidney Infection)?

Pyelonephritis is a potentially serious kidney infection that can spread to the blood, causing severe illness. Fortunately, pyelonephritis is almost always curable with antibiotics.

The main components of the urinary tract system are kidneys, ureters, bladder, and urethra. Any part of the urinary system may become infected and this is generally referred to as urinary tract infection (UTI). When a kidney becomes infected, the condition is medically referred to as pyelonephritis. Thus, Pyelonephritis (Kidney Infection) is only one of several types of infections encompassed by the term UTI.

Lower urinary tract infection involves the urethra, the bladder, and, in men, the prostate gland. The urethra is much shorter in women than in men, which is one reason why women are more vulnerable to UTIs and pyelonephritis.

What are the causes of  Pyelonephritis (Kidney Infection)?

Pyelonephritis is caused by a bacterium or virus infecting the kidneys. Though many bacteria and viruses can cause pyelonephritis, the bacterium Escherichia coli is often the cause. 

Typically, bacteria gain access to the urinary system from outside through the urethra (the drainage tube for urine from the bladder). The bacteria may then ascend in the urinary system and cause Pyelonephritis. Pyelonephritis (upper UTI) is typically more severe than lower UTI because bacteria may also infect the bloodstream (bacteremia) from the kidneys resulting in a more severe illness.

Who is at risk for  Pyelonephritis (Kidney Infection)?

People most at risk for pyelonephritis are those who have a bladder infection and those with a structural, or anatomic, problem in the urinary tract. Urine normally flows only in one direction—from the kidneys to the bladder. However, the flow of urine may be blocked in people with a structural defect of the urinary tract, a kidney stone, or an enlarged prostate—the walnut-shaped gland in men that surrounds the urethra at the neck of the bladder and supplies fluid that goes into semen. Urine can also back up, or reflux, into one or both kidneys. This problem, which is called vesicoureteral reflux (VUR), happens when the valve mechanism that normally prevents backward flow of urine is not working properly. VUR is most commonly diagnosed during childhood. Pregnant women and people with diabetes or a weakened immune system are also at increased risk of pyelonephritis.

In fact, 2% to 8% of pregnant women may have urinary infections during their pregnancy. This may occur because of slower transit of urine in the ureters during pregnancy from the pressure applied by the enlarging uterus.

In men, prostate enlargement is the main risk factor for UTI and Pyelonephritis.

Diabetes mellitus may also increase the risk of Pyelonephritis in both men and women.

Urinary stents placed in ureters to relieve obstruction due to stents or tumors are also a potential risk for Pyelonephritis. As matter of fact, any instrumentation or procedure of the urinary system (stenting, cystoscopy, biopsy, and transurethral resection of the prostate (TURP) can pose a risk for infection of the urinary tract.

Symptoms of  Pyelonephritis (Kidney Infection)

At least half of women have experienced the discomfort with urination caused by a urinary tract infection: painful, urgent, or frequent urination.

Pyelonephritis may start with similar symptoms. However, once the infection has spread to the kidney, signs of more severe illness usually result:

  • Back pain or flank pain
  • Fever (usually present) and/or chills
  • Feeling sick (malaise)
  • Nausea and vomiting
  • Confusion (especially in the elderly)
Pyelonephritis may cause noticeable changes in the urine, such as:

How is Pyelonephritis (Kidney Infection) diagnosed?

The tests used to diagnose pyelonephritis depend on the patient’s age, gender, and response to treatment and include the following:


Urinalysis is testing of a urine sample. The urine sample is collected in a special container in a health care provider’s office or commercial facility and can be tested in the same location or sent to a lab for analysis. The presence of white blood cells and bacteria in the urine indicate infection.

Urine culture

A urine culture is performed by placing part of a urine sample in a tube or dish with a substance that encourages any bacteria present to grow. The urine sample is collected in a special container in a health care provider’s office or commercial facility and sent to a lab for culture. Once the bacteria have multiplied, which usually takes 1 to 3 days, they can be identified. The health care provider can then determine the best treatment.


Ultrasound uses a device, called a transducer, that bounces safe, painless sound waves off organs to create an image of their structure. The procedure is performed in a health care provider’s office, outpatient center, or hospital by a specially trained technician, and the images are interpreted by a radiologist—a doctor who specializes in medical imaging; anesthesia is not needed. The images can show obstructions in the urinary tract. Ultrasound is often used for people who do not respond to treatment within 72 hours.

Computerized tomography (CT) scan

CT scans use a combination of x rays and computer technology to create three-dimensional (3-D) images. A CT scan may include the injection of a special dye, called contrast medium. CT scans require the person to lie on a table that slides into a tunnel-shaped device where the x rays are taken. The procedure is performed in an outpatient center or hospital by an x-ray technician, and the images are interpreted by a radiologist. Anesthesia is not needed. CT scans can show obstructions in the urinary tract. The test is often used for people who do not respond to treatment within 72 hours.

Voiding cystourethrogram (VCUG)

A VCUG is an x-ray image of the bladder and urethra taken while the bladder is full and during urination, also called voiding. The procedure is performed in an outpatient center or hospital by an x-ray technician supervised by a radiologist, who then interprets the images. Anesthesia is not needed, but sedation may be used for some people. The bladder and urethra are filled with contrast medium to make the structures clearly visible on the x-ray images. The x-ray machine captures images of the contrast medium while the bladder is full and when the person urinates. This test can show abnormalities of the inside of the urethra and bladder and is usually used to detect VUR in children.

Digital rectal examination (DRE)

A DRE is a physical exam of the prostate that is performed in the health care provider’s office. Anesthesia is not needed. To perform the exam, the health care provider asks the person to bend over a table or lie on his side while holding his knees close to his chest. The health care provider slides a gloved, lubricated finger into the rectum and feels the part of the prostate that lies in front of the rectum. Men with suspected pyelonephritis may have a DRE to determine whether a swollen prostate may be obstructing the neck of the bladder.

Dimercaptosuccinic acid (DMSA) scintigraphy

DMSA scintigraphy is an imaging technique that relies on the detection of small amounts of radiation after injection of radioactive material. Because the dose of radioactive material is small, the risk of causing damage to cells is low. The procedure is performed in an outpatient center or hospital by a specially trained technician, and the images are interpreted by a radiologist. Anesthesia is not needed. Radioactive material is injected into a vein in the person’s arm and travels through the body to the kidneys. Special cameras and computers are used to create images of the radioactive material as it passes through the kidneys. The radioactive material makes the parts of the kidney that are infected or scarred stand out on the image. DMSA scintigraphy is used to show the severity of kidney infection or kidney damage, such as scarring.

How is Pyelonephritis (Kidney Infection) treated?

Pyelonephritis is treated with antibiotics, which may need to be taken for several weeks. While a urine sample is sent to a lab for culture, the health care provider may begin treatment with an antibiotic that fights the most common types of bacteria. Once culture results are known and the bacteria is clearly identified, the health care provider may switch the antibiotic to one that more effectively targets the bacteria. Antibiotics may be given through a vein, orally, or both. Urinary tract obstructions are often treated with surgery.

Severely ill patients may be hospitalized and limited to bed rest until they can take the fluids and medications they need on their own. Fluids and medications may be given intravenously during this time.

In adults, repeat urine cultures should be performed after treatment has ended to make sure the infection does not recur. If a repeat test shows infection, another 14-day course of antibiotics is prescribed; if infection recurs again, antibiotics are prescribed for 6 weeks.

Home remedy with oral antibiotics and adequate water and fluid intake are usually sufficient for curing uncomplicated Pyelonephritis and urinary tract infection. Nondrug home therapy with fluid intake, cranberry products, or acupuncture without antibiotics is not advisable for Pyelonephritis.

Self-medication for Pyelonephritis is considered only in patients with mild, recurrent urinary infections. In individuals who are reliable and familiar with the symptoms of Pyelonephritis, appropriate antibiotics prescribed to them in advance by their treating physicians may be started at the onset of their symptoms.

Acute and Chronic Pyelonephritis

Most cases of pyelonephritis are acute, meaning sudden and self-limited. After cure with antibiotics, there is rarely any lasting damage to the kidneys. Most people do not develop pyelonephritis again.

Chronic (long-lasting) pyelonephritis is a rare condition, usually caused by birth defects in the kidney. Repeated UTIs (usually in children) result in progressive damage and scarring in the kidney. This can eventually cause kidney failure. Usually, chronic pyelonephritis is discovered in childhood.

Pyelonephritis Prevention

To help prevent pyelonephritis if you have had a previous episode or are at risk:

Drink several glasses of water each day. Water discourages the growth of infection-causing bacteria by flushing out your urinary tract. This flushing also helps to prevent kidney stones, which can increase the risk of pyelonephritis.

If you are a woman, wipe from front to back. To prevent the spread of intestinal and skin bacteria from the rectum to the urinary tract, women should always wipe toilet tissue from front to the back after having a bowel movement or urinating.

Try to urinate every 2 to 4 hours.

Empty your bladder completely when you urinate.

Women should avoid prolonged sitting in wet clothes.

Decrease the spread of bacteria during sex. Women should urinate after sexual intercourse to flush bacteria from the bladder. Some women who have frequent urinary tract infections after sexual activity can take antibiotics around the time of intercourse to prevent an infection.

If there is a structural problem with the urinary system, such as blockage from a stone, or a developmental abnormality, surgery can be done to restore normal urinary function and prevent future episodes of pyelonephritis.

Points to Remember

Pyelonephritis is a type of urinary tract infection that affects one or both kidneys.

Pyelonephritis is caused by a bacterium or virus infecting the kidneys. Though many bacteria and viruses can cause pyelonephritis, the bacterium Escherichia coli is often the cause. Bacteria and viruses can move to the kidneys from the bladder or can be carried through the bloodstream from other parts of the body.

Symptoms of pyelonephritis can vary depending on a person’s age and may include the following:
  • fever
  • vomiting
  • back, side, and groin pain
  • chills
  • nausea
  • frequent, painful urination
Children younger than 2 years old may only have a high fever without symptoms related to the urinary tract. Older people may not have any symptoms related to the urinary tract either; instead, they may exhibit confusion, disordered speech, or hallucinations.

Most people with pyelonephritis do not have complications if appropriately treated with bacteria-fighting medications called antibiotics.