Understanding Pyelonephritis: An Infection of the Kidneys

Pyelonephritis is not your usual garden-variety UTI

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UTI implies an infection of the urinary tract.  The urinary tract in turn is defined as everything down from the kidneys, all the way to the tip of the urethra where the urine is eventually excreted from the body.  Therefore, the term UTI is an umbrella catchall phrase that could imply infection of any of these parts.  Polynephritis, is a specific term which implies infection of the kidneys.  Therefore its a type of a UTI which involves the kidneys.

Either one or both kidneys might be affected.


Pyelonephritis is not your usual uncomplicated UTI.  Technically, any UTI can progress to involve the kidneys and therefore turn into full blown pyelonephritis.  However, certain groups are higher risk. Here is a non-inclusive list:

In general, anything that interferes with the normal unidirectional flow of urine increases the risk of pyelonephritis.


Most patient would be sicker than the average "uncomplicated" UTI patient.

 Hence symptoms could include:

  • Back pain
  • High fever
  • Nausea, vomiting
  • Pain with urination
  • Urgency
  • Chills


Some of the tests needed to diagnose pyelonephritis are the same as what one would use to diagnose any other urinary tract infection.  Hence blood test looking for signs of infection like elevated white cell counts could be helpful.

 However, the urine is really where the money is.  Typically, a midstream clean-catch urine specimen is obtained.  Initial screening test that might be done include the dipstick test which could indicate signs of infection in the urine (including elevation of white cell count in the urine, bacteria, or other abnormal substances like nitrates or esterase in the urine).

The infection can however be confirmed mostly by a urine culture where the infection-causing bacteria is grown on artificial media.  This is important not just for diagnostic purposes, but also helps in fine-tuning the treatment since it gives us a pretty good idea about the which antibiotic could be useful for treatment.

In most clinical situations, a combination of symptoms and the diagnostic tests mentioned thus far are usually enough to make a reasonable diagnosis.  However, if the diagnosis is still in doubt, further imaging test to confirm the site of infection can be done.  These tests include ultrasounds, CT scans (to look for obstruction) and finally a study called Dimercaptosuccinic acid (DMSA) scintigraphy where a radioactive dye is given to the affected patient.

Uptake of this radioactive dye makes the infected site (in this case the kidney) stand out on imaging.  However, in the real world scenario, this test is seldom required.


Unlike the routine uncomplicated UTI, pyelonephritis does need to be taken a bit more seriously and treated with a tad more aggression.  While one episode should not usually cause any lasting complications (assuming it's treated in an appropriate manner), repeated episodes can sometimes cause permanent scarring in the kidneys and therefore bring the onset of chronic kidney disease because of renal tissue scarring.  

The other concern is about the spread of infection from the kidney into the blood, a phenomenon called sepsis which is a serious condition that would typically require treatment in an intensive care setting.


Treatment of pyelonephritis is similar to treatment of urinary tract infections but typically will require longer and stronger antibiotic courses.  Some patients will require hospitalization as well so that intravenous fluids can be administered.  Pain and fever control are also essential using symptomatic treatments.

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