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Overview

What Is Pyelonephritis?

Pyelonephritis is a kidney infection that causes inflammation in one or both kidneys. It often begins as a bladder infection that travels upward through the urinary tract to the kidneys. Bacteria are the most common cause, and people of any age can develop this condition. Unlike a lower urinary tract infection, pyelonephritis can cause whole-body symptoms such as fever, chills, and feeling very unwell.

Symptoms

Pyelonephritis Symptoms

  • Pain in the flank or back, usually on the side of the affected kidney.
  • Fever.
  • Chills or shaking chills.
  • Painful urination (dysuria).
  • Frequent urination.
  • Nausea.
  • Vomiting.
  • Cloudy urine.
  • Bloody urine (hematuria).

Seek care promptly

Symptoms can worsen quickly

Sudden fever with flank pain, vomiting, confusion, or a feeling of severe illness can signal a serious kidney infection. Seek urgent medical attention rather than waiting for symptoms to improve on their own.

Causes

Causes of Pyelonephritis

Pyelonephritis usually starts when bacteria, often from the digestive tract, enter the urethra and cause a urinary tract infection. The bacteria can move from the bladder through the ureters and reach the kidneys, where they cause infection and inflammation. This upward spread is the most common way a kidney infection develops.

  • Bacteria can spread to the kidneys through the bloodstream from an infection elsewhere in the body, although this is less common.
  • A urinary blockage, such as from a stone or narrowing, can prevent urine from flowing normally and allow bacteria to multiply.
  • Urine may flow backward toward the kidneys, a problem called vesicoureteral reflux, increasing the risk of infection.
  • Urinary devices such as catheters can introduce bacteria or provide a path for them to enter the urinary tract.

Risk Factors

Risk Factors for Pyelonephritis

  • Being female increases risk because the urethra is shorter and bacteria can reach the bladder more easily.
  • Pregnancy can affect urine flow and makes a kidney infection more concerning for both the pregnant person and fetus.
  • A history of urinary tract infections increases the chance of another infection reaching the kidneys.
  • Urinary tract abnormalities can interfere with normal urine flow or allow urine to move backward toward the kidneys.
  • Kidney or bladder stones can block urine flow and make infection more difficult to clear.
  • Urinary blockage from another cause can allow bacteria to remain in the urinary tract.
  • Using a urinary catheter can increase the risk of introducing bacteria.
  • Diabetes can increase infection risk and may make infections more difficult to control.
  • A weakened immune system can reduce the body’s ability to fight urinary infections.
Risk-factor typeExamples
Factors a person may be able to modify or manageCatheter care, diabetes control, prompt treatment of urinary symptoms, and medical management of stones or blockage.
Factors that are non-modifiable or medically determinedFemale urinary anatomy, pregnancy, urinary tract abnormalities, recurrent infections, and some immune or kidney conditions.

Complications

Pyelonephritis Complications

  • Sepsis can occur when the infection triggers a dangerous whole-body response.
  • A kidney abscess is a collection of infected fluid that may require drainage.
  • Kidney scarring or damage can develop after severe, untreated, or repeated infections.
  • Recurrent infections can lead to additional illness and increase the risk of lasting kidney problems.
  • During pregnancy, a kidney infection can cause complications that require prompt medical treatment and monitoring.

Emergency concern

Know the signs of severe infection

Confusion, rapid breathing, faintness, severe weakness, or very low blood pressure can indicate sepsis. Call emergency services or go to an emergency department immediately if these symptoms occur.

Diagnosis

How Pyelonephritis Is Diagnosed

Clinicians assess your symptoms, medical history, temperature, and overall condition, and may check for tenderness in the back or side. A urinalysis can show signs of infection, while a urine culture helps identify the responsible bacteria and guide antibiotic selection. The clinician may also look for factors such as a blockage, stone, pregnancy, or another condition that could affect treatment.

  • Blood tests can assess inflammation, kidney function, and how seriously the body is responding to the infection.
  • Blood cultures may be used when illness is severe or bacteria may have entered the bloodstream.
  • Ultrasound or CT imaging may be recommended to look for a urinary blockage, stone, abscess, or other complication.
  • A pregnancy test may be performed when pregnancy is possible because it affects evaluation and treatment choices.

Treatment & Management

Pyelonephritis Treatment and Management

Prescription antibiotics are the main pyelonephritis treatment. The choice and duration depend on the urine culture, the bacteria involved, local resistance patterns, and how severe the illness is. Take the full course exactly as prescribed, even if you begin to feel better before the medication is finished.

  • Stable patients who can drink and take medicine may receive oral antibiotics at home with follow-up as directed.
  • People with severe illness, persistent vomiting, sepsis, or other complications may need intravenous antibiotics and hospital care.
  • Fluids, rest, and clinician-approved medicines for pain or fever can support recovery, but they do not replace antibiotics.
  • A procedure may be needed to relieve a urinary blockage or drain a kidney abscess so the infection can clear.

Prevention

Can Pyelonephritis Be Prevented?

  • Drink adequate fluids when medically appropriate for you and your health conditions.
  • Do not regularly delay urination when you feel the need to go.
  • Wipe from front to back after using the toilet to help reduce the spread of bacteria.
  • Urinating after sex may help clear bacteria from the urethra for some people.
  • Seek medical care for urinary symptoms so a bladder infection can be treated before it spreads.

People with recurrent infections, kidney or bladder stones, urine reflux, or a urinary blockage may need an individualized prevention plan. This may include treating the underlying problem, monitoring for infections, or using other strategies recommended by a clinician rather than relying only on home measures.

Outlook and Prognosis

Outlook and Prognosis

Most people improve with prompt, appropriate treatment, although recovery may take longer when the infection is severe, recurrent, or linked to an obstruction or another health condition. Completing the prescribed antibiotics and attending follow-up can reduce the risk of persistent infection and kidney damage. A clinician may recommend additional care when infections keep returning.

  • Delayed treatment can allow the infection to spread or cause lasting kidney problems.
  • Sepsis is associated with a more serious illness and requires emergency treatment.
  • A urinary blockage can prevent antibiotics from fully clearing the infection until the blockage is treated.
  • A kidney abscess may require drainage and can prolong recovery.
  • Repeated infections can increase the risk of kidney scarring or damage.
  • Underlying kidney disease can make treatment and recovery more complex.

When Should You See a Doctor

When Should You See a Doctor for Pyelonephritis?

Contact a clinician

Kidney infection symptoms need prompt evaluation

Seek same-day medical care for fever or chills with back or side pain, painful urination with whole-body symptoms, vomiting that prevents you from keeping down fluids or medicines, blood in the urine, or urinary symptoms during pregnancy.

Emergency care

Get help for signs of severe infection

Go to emergency care for confusion, fainting, severe weakness, trouble breathing, severe dehydration, or rapidly worsening symptoms. These signs may indicate sepsis or another serious complication.

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