Pyelonephritis is also known as kidney infection , this refers to inflammation of the renal parenchyma and urinary tract due to certain infectious process that usually originate in the urethra  and the bladder and upward through the ureters arrive to the kidneys .

Classification of pyelonephritis

Acute pyelonephritis is classified as uncomplicated and complicated:

  1. Acute uncomplicated pyelonephritis: inflammation of the kidney tissue due to infection by bacteria or common pathogens, which occurs in patients with a healthy immune system (immunocompetent) and whose kidney function is normal.
  2. Complicated acute pyelonephritis: inflammation of the kidney tissue in people who have conditions that can modify the body’s response to infection or people who have risk factors that increase the organ’s susceptibility to infection, risk factors will be discussed later.

Symptoms of Pyelonephritis 

The symptoms and signs that a patient with pyelonephritis presents are usually very characteristic:

  • Fever.
  • Shaking chills.
  • Nausea and vomiting
  • Pain in the lumbar region (lower back), in the flanks and iliac fossa (lateral and lower regions of the abdomen).
  • Groin pain
  • Desire to urinate constantly but not being able to do so.
  • Burning or pain when urinating.
  • Blood or pus in the urine.
  • Foul-smelling or foul-smelling urine.

In case of presenting any of these symptoms, do not hesitate to consult your doctor, since poorly treated urinary infections can have great consequences for your urinary system and a timely diagnosis will be of great help.

The diagnosis of pyelonephritis is based on the results of uroculture (urine culture) that shows the presence of more than 10,000 Colony Forming Units, known as CFU by its acronym, in addition to the presence of symptoms compatible with the pathology.


The main cause of pyelonephritis , as previously mentioned, is the rise of bacteria found in the urethra and bladder to the kidneys, said rise through the ureters. In some cases, the spread of the bacteria is hematogenous , that is, the bacteria are transported by the blood to the kidneys, but this is usually uncommon, however this possibility is not ruled out.

On the other hand, we have risk factors, which, as we said at the beginning of the text, would be mentioned later. These are considered causes of pyelonephritis, because thanks to the presence of one or more of them, the chances of this pathology being triggered are much higher.

Risk factor’s 

  • Female Sex: the fact of being a woman is a risk factor, because their urethra is shorter than that of men, which facilitates the ascent of bacteria. In addition to this, the vaginal orifice and the anus are very close to the urethra, increasing the amount of bacteria that could reach it.
  • Obstructions of the urinary tract: any alteration that does not allow adequate urine output is considered an obstruction, for example kidney stones, an enlarged prostate in men or even congenital defects in the urinary system. What happens is that by not having an adequate flow of urine, it will be collected and the proliferation of possible bacteria will increase. 
  • Immunosuppressed patients: this means that patients who suffer from diseases that for some reason alter the body’s defense system ( immune system ) such as HIV, cancer patients, etc. They will not be able to fight against the bacteria that cause the infection in the same way as a totally healthy person.
  • Neurogenic bladder: it is evidenced many times in diabetic patients, what happens in this pathology is that the nerves that send signals to the bladder to be able to urinate are damaged, so urine is not disposed of properly, bacterial proliferation increases and therefore this is a risk factor for the rise of said bacteria and the development of pyelonephritis.
  • Urinary catheters: catheters are medical devices used to help the patient excrete urine, these are found within the urinary tract (urethra, bladder even some can reach the renal pelvis) and this is a surface to which bacteria are they adhere and proliferate.

As could be noted, any foreign body (catheters, probes, stones, etc.) within the urinary tract is a risk factor for developing infections.

This is because the bacteria bind to them and as explained above, they proliferate and ascend to the kidney. The same happens when there are alterations in the morphology or anatomy of these pathways.

By Dr. Eric Jackson

Dr. Eric Jackson provides primary Internal Medicine care for men and women and treats patients with bone and mineral diseases, diabetes, heart conditions, and other chronic illnesses.He is a Washington University Bone Health Program physician and is a certified Bone Densitometrist. Dr. Avery is consistently recognized in "The Best Doctors in America" list.

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