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Acute pyelonephritis

Acute Kidney Infection, Acute Pyelitis, Acute Pyonephrosis

What is Acute pyelonephritis?

Acute pyelonephritis is one of the most common renal diseases. It is an inflammation of the kidney characterized by the sudden onset (within one to two days) of fever and chills, side pain, and frequent, painful urination. Acute pyelonephritis results most commonly from the spread of a naturally occurring lower urinary tract or bladder infection up through the ureters to the kidneys. It may also be caused by catheterization or bladder surgery, from a blood infection (such as sepsis or endocarditis), or possibly from lymphatic infection. Additionally, individuals experiencing difficulty emptying their bladder (neurogenic bladder) or those with a urinary tract obstruction or stricture are at a high-risk of developing acute pyelonephritis.

Finally, individuals with a congenital weakness of a juncture between the bladder and ureter may experience a condition known as vesicoureteral reflux in which urine backs up from the bladder into the ureters and kidneys.

This condition affects females much more than males. This is presumably due to the fact that females have a shorter urethra with closer proximity to the vagina and rectum, which allow bacteria greater access. Also, females lack an antibacterial secretion, which is produced in males. Disease incidence increases with age, and sexually active and pregnant women, diabetics, and persons with other renal diseases are at the greatest risk of developing this condition.

How is it diagnosed?

Acute pyelonephritis signs and symptoms

Sudden onset of:

  • High fever (102° F or higher and shaking chills.
  • Burning, frequent urination.
  • Cloudy urine or blood in the urine.
  • Aching (sometimes severe) in one or both sides of the lower back.
  • Abdominal pain.
  • Marked fatigue.

Note: Young children and the elderly may not have typical symptoms or signs.

If a physician suspects a kidney infection the patient's medical history is normally compiled. The physician may ask questions about the patient's toilet habits and previous urinary tract infections. A physical examination will be performed including taking the temperature and feeling (palpating) the abdomen for tender, painful areas.

A number of diagnostic tests may be performed, including:

  • Urinalysis. Also known as a rapid urine test or diastick test. A urine sample is collected to check for white blood cells (leukocytes), red blood cells (erythrocytes), protein and bacteria in the urine. Collection is most often done by “clean-catch” where a patient provides a sample of mid-stream urine in a sterile cup. For those with acute uncomplicated infections, a urinalysis is generally sufficient to diagnose the infection.
  • Urine culture. This is a laboratory test of a urine sample to detect the presence of bacteria that is not readily identified as amounts signifiying an infection. It is also useful for detecting the particular type of bacteria responsible for the infection.
  • Urine sensitivity. This test is used when the bacteria responsible for the infection may be restistant to antibiotics. It is used to identify which antibiotics are not useful due to restistace. The test uses samples of urine from the urine culture to test for the best antibiotic to prescribe.
  • Blood tests and imaging tests, such as an ultrasound, may also be required.

How is Acute pyelonephritis treated?

Since acute pyelonephritis is typically due to a urinary tract infection, antibiotics are the first line of therapy. Whenever it is possible to identify the type of bacteria causing the infection, antibiotics are prescribed which are specific for that organism. If the organism is not identified, a broad-spectrum antibiotic is prescribed.

Although, with treatment, bacteria are usually eliminated from the urine within two to three days, antibiotics are continued for a course of ten to fourteen days to make certain the infection is gone. A follow-up culture of the urine is completed one week after the end of drug therapy. In addition to antibiotics, an analgesic for pain relief and an antipyretic medication for fever reduction are also often prescribed. The individual is also instructed to force fluids in an effort to clear out the bacterial infection.

In some cases, an acid-ash diet may be recommended to prevent kidney stone formation.

Individuals experiencing infection as a result of obstruction or vesicoureteral reflux are typically less responsive to antibiotic treatment. In these cases, surgery may be necessary to relieve the obstruction or correct a structural problem. Individuals at high risk of experiencing disease recurrence include those with an indwelling catheter or those who are on some sort of maintenance antibiotic therapy.


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What might complicate it?

Complications that may be associated with acute pyelonephritis include renal damage, abscess, papillary necrosis, sepsis, and pyelonephrosis.

Predicted outcome

With proper treatment and follow-up care, most individuals recover quickly and completely, and extensive permanent damage is rare. Individuals with coexisting renal disease, however, may develop chronic pyelonephritis. Without treatment, symptoms disappear, however, residual infection usually remains and symptoms are likely to recur, possibly with greater severity.


Differential diagnoses include papillary necrosis, urinary stone, appendicitis, cholecystitis, pancreatitis, diverticulitis, epididymitis and acute prostatitis.

Appropriate specialists

Family practitioner, internist, urologist, radiologist, and microbiologist.

Last updated 12 July 2015