An Overview of Pyelonephritis (A Kidney Infection)

Male kidney anatomy, illustration

A kidney infection—called pyelonephritis—is a serious bacterial infection of one or both of your two kidneys, which are located in your lower back. The bacterial infestation causes the kidney to become inflamed, producing symptoms like fever, chills, lower back (flank) pain, nausea, and/or vomiting.

The diagnosis of pyelonephritis requires a medical history, physical examination, and various laboratory tests, most notably a urine culture. Antibiotic therapy, either at home or in a hospital (depending on how sick a person is), is the primary treatment of pyelonephritis.

Please note that a kidney infection is more serious than acute cystitis, which refers to bladder inflammation from a bacterial infection. Cystitis is what most people are referring to when discussing a urinary tract infection (UTI).


The typical symptoms of pyelonephritis include the following:

  • Flank pain (pain in the lower back where the kidneys are located)
  • Nausea
  • Vomiting
  • Fever
  • Chills

Patients with pyelonephritis may or may not also have symptoms of acute cystitis, which are pain on urination, cloudy urine, and urinary frequency and urgency. Abdominal and/or pelvic pain may also be present.

If left untreated, complications of pyelonephritis may develop, such as a blood infection (called sepsis) or an abscess within or surrounding the affected kidney. Emphysematous pyelonephritis, where the kidneys are damaged and gas builds up in the kidney, is another potential complication. 


A kidney infection occurs when bacteria, most commonly Escherichia coli, travels from the urethra up through the bladder and ureter into one or both of your kidneys. 

Most cases of pyelonephritis occur in young, healthy adult women, followed by infants and older adults. 

For healthy women, factors that increase their risk of developing pyelonephritis include the following:

  • Increased sexual activity (three or more times per week) in the prior 30 days
  • UTIs in the past year
  • Diabetes
  • Stress incontinence in the prior 30 days
  • New sexual partner in the prior year
  • Recent spermicide use
  • History of UTIs in the patient's mother


The diagnosis of pyelonephritis is based on a medical history and physical exam, as well as results from diagnostic tests, such as a urinalysis and urine culture.

Imaging isn't needed to diagnose most cases of pyelonephritis. That said, imaging with an ultrasound or CT scan can be useful if symptoms do not improve (there may be an alternative diagnosis) or to identify a structural abnormality or complication (e.g., an abscess around the kidney)

Medical History and Physical Examination

In addition to inquiring about symptoms of pyelonephritis, especially flank pain, fever, and nausea/vomiting, a healthcare provider will also check your vitals, including your body temperature.

A fever is often present in people with acute pyelonephritis—exceptions may include people with weakened immune systems or the elderly.

Your healthcare provider will also check for costovertebral angle (CVA) tenderness by tapping on the area of your lower back (just below the ribcage) which overlies your kidney.

If pain is elicited when your healthcare provider taps on this area, the diagnosis of pyelonephritis is supported.

Keep in mind, other conditions (for example, kidney stones) can cause CVA tenderness and in certain instances, especially obese individuals, it may be challenging to accurately access for CVA tenderness. 

Diagnostic Tests

Unlike acute uncomplicated cystitis, suspicion of pyelonephritis warrants a urine culture, in addition to a standard urinalysis.

Sometimes, mostly for patients who are hospitalized for pyelonephritis, blood cultures are obtained.

Additional laboratory tests may include:


The treatment of pyelonephritis involves the administration of both fluids and antibiotics.

Fluid and Antibiotic Administration

Since pyelonephritis is more likely than acute cystitis to be caused by an antibiotic-resistant bacteria, including strains of E. coli that are resistant to Bactrim (TMP-SMX), the treatment of pyelonephritis usually begins with an oral (by mouth) broad-spectrum antibiotic, like Cipro (ciprofloxacin) or Levaquin (levofloxacin).

If a person has a high fever, severe pain, or is unable to keep medicine, food, or fluids down due to persistent nausea and vomiting, hospitalization for intravenous (through the vein) administration of fluids and antibiotics is required.

Besides a severe infection or significant nausea and vomiting, other factors that usually warrant hospitalization for the treatment of pyelonephritis include:

  • Being pregnant
  • Male sex
  • Patients with structural or functional abnormalities of the urinary tract system
  • Predisposing medical condition (e.g., diabetes mellitus)
  • Symptoms or signs of sepsis or septic shock


While a serious infection, the upside is that there are some steps that you (a woman) can take to prevent pyelonephritis (and acute cystitis):

  • Drink plenty of water and urinate regularly
  • Urinate before and after sexual intercourse
  • Wipe from front to back so as to avoid the introduction of bacteria from your rectum unto your urinary tract
  • Take showers instead of baths
  • Avoid feminine hygiene products applied to the genital area like douches, sprays, and powders

A kidney infection can lead to serious, potentially life-threatening complications if not treated promptly. Therefore, if you are experiencing a fever and/or flank pain, even if you do not have symptoms of cystitis (e.g., urinary frequency or pain with urination), be sure to seek medical attention right away.

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Colgan R, Williams M, Johnson JR. Diagnosis and Treatment of Acute Pyelonephritis in Women. Am Fam Physician. 2011 Sep 1;84(5):519-26.

  2. Scholes D, Hootin TM, Roberts PL, Gupta K, Stapleton AE, Stamm WE. Risk Factors Associated with Acute Pyelonephritis in Healthy Women. Ann Intern Med. 2005 Jan 4;142(1):20-27.

  3. Faust JS, Tsung JW. Eliciting renal tenderness by sonopalpation in diagnosing acute pyelonephritis. Crit Ultrasound J. 2017;9:1. doi: 10.1186/s13089-016-0056-6

  4. Gupta K et al. International clinical practice guidelines for the treatment of acute uncomplicated cystitis and pyelonephritis in women: A 2010 update by the Infectious Diseases Society of America and the European Society for Microbiology and Infectious Diseases. Clin Infect Dis. 2011 Mar 1;52(5(:e103-20. doi: 10.1093/cid/ciq257

  5. Centers for Disease Control and Prevention. (2015). Urinary Tract Infection.

Additional Reading
  • Keenan DB, O'Rourke DM, Courtney AE. Pyelonephritis can lead to life-threatening complications. Practitioner. 2017 Feb;261(1801):17-20.

  • Gupta K, Trautner BW. Urinary Tract Infections, Pyelonephritis, and Prostatitis. In: Kasper D, Fauci A, Hauser S, Longo D, Jameson J, Loscalzo J. eds. Harrison's Principles of Internal Medicine, 19e. New York, NY: McGraw-Hill; 2015.
  • Howes DS, Bogner MP. Chapter 94. Urinary Tract Infections and Hematuria. In: Tintinalli JE, Stapczynski J, Ma O, Cline DM, Cydulka RK, Meckler GD, T. eds. Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 7e. New York, NY: McGraw-Hill; 2011.

By Naveed Saleh, MD, MS
Naveed Saleh, MD, MS, is a medical writer and editor covering new treatments and trending health news.