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Pyelonephritis - Causes, Risk Factors, Symptoms, Diagnosis, and Treatment

Published on Sep 28, 2022 and last reviewed on May 11, 2023   -  8 min read


Pyelonephritis or kidney infection occurs when bacteria or virus enters the urinary system through the urethra. Read the article to learn more about it.


A urinary tract infection occurs when bacteria invade the organs of the urinary system. As a result, the patient presents with the symptoms of pain, the presence of blood in the urine, a burning sensation while urinating, and restricted urine flow. The different types of urinary tract infections are listed below:

  1. Cystitis (bladder infection).

  2. Urethritis (urethral infection).

  3. Pyelonephritis (kidney infection).

  4. Vaginitis (vaginal infection).

Urinary tract infection is a common condition and requires medical attention. The bacteria enter the urinary tract mainly through the rectum (the organ that holds stools). They get attached to the surface of the urinary tract, multiply and form colonies. After this, they enter the urinary bladder through the urinary and finally migrate upwards to infect the ureters and kidneys. Pyelonephritis presents with severe complications if left untreated.

What Is Pyelonephritis?

The inflammation of the kidneys that occurs due to bacterial infection is known as pyelonephritis. It is commonly seen in women and can cause permanent damage to the kidneys if not treated at the right time. The bacteria named Escherichia coli (E.Coli) is the main culprit behind the infection in the majority of the cases. It resides in the body, mainly in the intestines, without causing any harm and is not found in the urinary system.

However, it enters the urethra through stools and infects the other organs of the urinary system. It does not remain confined to the urinary system alone but migrates to the bloodstream through the kidneys. The condition becomes life-threatening because the bacteria-infected blood reaches the other organs, resulting in their damage.

What Are the Organs of the Urinary System?

The organs comprising the urinary system, along with their functions, are listed in the table below:


What Are the Causes of Pyelonephritis?

There are several microorganisms residing in the digestive system of the human body, and most of them do not cause any harm. These organisms do not have access to the urinary system under normal conditions. There are a variety of immune cells present within the urinary system that does not allow the bacteria to enter. Most of the bacteria are flushed out in the urine formed by the kidneys, and this is how the urinary system saves itself from any infection.

However, the bacteria that originate from the gut threaten the urinary system, and one such bacteria is Escherichia coli (E.Coli). Bacterial molecules (virulence factors) expressed by Escherichia coli (E.Coli) help infect the urinary system. It enters the urethra through stools and finally reaches the kidneys infecting them. Some other viruses and bacteria infect the kidneys, but in 90 percent of the cases of pyelonephritis, Escherichia coli (E.Coli) is the causative organism.

What Are the Risk Factors for Pyelonephritis?

The risk factors for pyelonephritis are listed below:

  • Urinary Tract Obstruction: Urinary tract obstruction means some blockage that does not let the urine flow freely. As a result, the urine remains in the body and provides a medium for bacterial growth, thereby increasing the risk of infection. The blockage can occur in any urinary system organs, including kidneys, ureters, urinary bladder, and urethra. The presence of tumors, kidney stones, and enlargement of the prostate gland are some of the causes of urinary tract obstruction.

  • Weak Immune System: Immune system works to protect the body from diseases and fight infection-causing organisms. However, conditions like diabetes-acquired immunodeficiency syndrome (AIDS) and drugs such as Azathioprine and Methotrexate weaken and reduce the abilities of the immune system to fight infections.

  • Use of a Catheter: A tube inserted by the doctor after the diagnostic or surgical procedure to facilitate the passage of urine is known as a catheter. If the catheter remains in the body for a long, especially in bed-ridden patients, it increases the risk of kidney infection.

  • Bladder Nerve Damage: If the nerves present between the brain and the bladder get damaged, the person does not feel any bladder sensations causing the infection to spread rapidly to the kidneys. The nerves mainly get damaged due to spinal cord injury.

  • Females Are at Risk: Women are at a higher risk of suffering from urinary tract infections than men. It is because the urethra (the tube that carries urine outside the body) is located close to the anus (the organ that allows the stools to leave the body) in females. This makes it easier for the bacteria to enter the urinary system and cause infection.

  • Vesicoureteral Reflux: The urine flows back to the ureters from the urinary bladder instead of flowing out of the body. The backflow of urine increases the risk of infection to a large extent.

What Are the Symptoms of Pyelonephritis?

The following symptoms are seen in the case of pyelonephritis:

  1. The patient usually presents with chills and a fever over 102 degrees Fahrenheit (38.8 degrees Celsius) due to infection.

  2. Presence of severe pain in the lower back, abdomen, and flank region.

  3. Presence of pus and blood in the urine (hematuria).

  4. The pain often becomes unbearable and causes uneasiness (nausea) followed by vomiting.

  5. The patient frequently rushes to the bathroom because of the constant urge to urinate. However, even after urinating, the person feels that the bladder is not empty and finds it difficult to pass urine.

  6. Presence of pain or burning sensation while urinating.

  7. The urine smells bad and appears cloudy.

What Are the Methods of Diagnosis of Pyelonephritis?

The following methods are used to diagnose pyelonephritis:

  • Filling a Medical History Form: The medical history form consists of questions about the health of the patient, the symptoms and the time of their onset, the medications and the previous treatments undergone by the patient, and if the patient has experienced the condition before. This gives the doctor an idea about the health of the patient and the condition he is suffering from.

  • Physical Examination: The doctor inserts a gloved finger into the rectum to examine the wall of the prostate gland, and it is known as a digital rectal examination. If the prostate gland is swollen, it can block the urinary tract and cause infection in men.

  • Urinalysis: In this test, the urine collected by the patient is examined under a microscope in the laboratory. In case of infection, high amounts of white blood cells will be present in the urine.

  • Blood Test: The doctor might ask the patient to undergo a blood test to determine the severity of the condition. The infection spreads to the blood if the bacteria multiply rapidly. So the blood test helps the doctor rule out blood infection.

Imaging Tests:

The following imaging tests are also done to diagnose kidney infection:

  1. Computed Tomography (CT Scan): In this test, 3-dimensional (3D) images of the kidneys are obtained on the computer. The X-ray images obtained do not provide many ideas about the infection, but the blockage present in the urinary system can be detected.

  2. Renal and Bladder Ultrasound: In this procedure, sound waves are sent to the kidney, and images of the kidney, ureters and urinary bladder are obtained. The doctor looks at the images on the computer. This image will give him an idea about the presence of stones, tumors, wounds, or anything that leads to the blockage of the urinary system.

  3. Voiding Cystourethrogram: This test is mainly done to check if the patient is urinating correctly or if any backflow of urine from the bladder to the kidneys. In this test, a tube is passed into the bladder of the child, and a solution is injected through this tube into the bladder. The doctor will check if any amount of solution is flowing backward to the kidney or if any blockage is present in the passage of urine.

  4. Dimercaptosuccinic Acid Scintigraphy (DMSA Scan): It is the "gold standard" for diagnosing pyelonephritis. In this procedure, a special material is injected into the body through veins. The images of the kidneys are obtained through the special camera known as the gamma camera. It is used to detect the presence of infection or scars in the kidneys.

What Are the Treatment Options for Pyelonephritis?

The treatment options for pyelonephritis are listed below:

  • Antibiotics: Pyelonephritis is an infection of the kidneys, so antibiotics remain the first choice. The type of drug prescribed by the doctor depends on the health of the patient and the bacterial strain that caused the infection. If the lab tests identify the bacteria, the doctor might change the drugs. The commonly prescribed drugs are Ciprofloxacin, Ampicillin, Cotrimoxazole, Amoxicillin, and Clavulanic acid combination. The infection usually subsides in two to three days, but the patient needs to continue with the medications for 14 days to complete the course.

  • Hospitalization: If the infection is severe and does not subside even after completing the entire course of antibiotics (14 days), the patient needs to be hospitalized. The fluids and drugs are injected into the body through the veins. The blood and urine levels are monitored until the infection subsides.

  • Surgery: If the infection occurs repeatedly and does not respond to antibiotics, surgery is required to treat the condition. If the infection is due to some defect or blockage in the urinary system, the doctor performs surgery to remove the condition. In severe cases, a nephrectomy might be done. In this procedure, all or some parts of the kidneys are removed.

How to Prevent Pyelonephritis?

Pyelonephritis can be prevented in the following ways:

  1. Stay Hydrated: It is important to drink plenty of water daily to expel the waste products from the body. In addition, a patient must drink more than eight to ten glasses of water if he suffers from kidney stones and urinary tract infections.

  2. Healthy Bladder Habits: Sometimes, it is seen that people hold urine and do not go to the restroom. The patient must pass urine as soon as he feels the need to do so to avoid urinary infections.

  3. Wiping Properly: Women must wipe properly after passing urine to prevent the bacteria from entering the vagina.

What Are the Complications of Pyelonephritis?

The complications of pyelonephritis are listed below:

  • If the infections persist for a prolonged time, the bacteria might enter the blood, causing blood poisoning or septicemia. The other organs of the body also get affected and become a medical emergency.

  • If the condition is left untreated, the kidneys become scarred, resulting in high blood pressure, kidney disease, and permanent kidney damage.

  • In patients suffering from diabetes and kidney infection, toxic gasses accumulate in the kidney tissues and damage them. This condition is known as emphysematous pyelonephritis.

  • If the infection is present during pregnancy, the woman is at risk of delivering low birth weight babies.


Pyelonephritis or kidney infection requires medical care and attention. The condition becomes severe and life-threatening if the infection spreads to the blood. It is important to take care of the urinary system to prevent the disease. If the patient notices symptoms like pain, burning sensation while urinating, and fever, he must consult the doctor immediately. The infection can be treated with antibiotics alone, and surgery is required in rare cases. One needs to drink plenty of water, have a nutritious diet and follow healthy bowel and bladder habits to prevent infection and live a healthy life.

Last reviewed at:
11 May 2023  -  8 min read




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