What is pyelonephritis?

pyelonephritis is inflammation of the kidneys. The most common cause is a bacterial infectionwhich is why it is also known as kidney infection or upper urinary tract infection. The infection is usually caused by the ascent of pathogens through the urinary tract, although in some cases they can also reach through the bloodstream.

The most common symptoms are high fever, flank pain, nausea, burning and stinging when urinating, and frequent urination. If left untreated, it can be complicated by sepsis and kidney failure. Treatment consists of administering antibiotics; In severe cases, hospitalization of the patient may be necessary.

Pyelonephritis is quite common, especially in adult women among which there is a prevalence between 1 and 2 per thousand compared to 0.5 per thousand among men. Although treatment is usually effective and has a good prognosis, in elderly patients the risk of death from kidney failure can reach 40%.

Most prominent symptoms

The symptoms of pyelonephritis usually appear quickly, in a few hours or a day. It usually includes a high fever, pain when urinating, and abdominal pain radiating to the sides of the back. Nausea and vomiting are also common symptoms.

Chronic pyelonephritis causes persistent abdominal pain and frequently appears blood in urine. Proteins related to inflammatory processes can accumulate in tissues and trigger AA amyloidosis.

In advanced pyelonephritis, signs of septic shock such as rapid breathing, drop in blood pressure, and even delusions.


The most common cause of pyelonephritis is due to invasion of the urinary tract by common bacteria in the digestive tract. Escherichia coli is the most common (70-80%), followed by others such as Enterococcus faecalis. In hospital-acquired pyelonephritis, other bacteria such as Pseudomonas aeruginosa, Kiebsiella and coliform bacteria.

Most cases of pyelonephritis begin as a lower urinary tract infection that progresses to the bladder and then to the kidneys. The risk increases with the following factors:

  • mechanical factors: structural alterations of the urinary tract, vesicoureteral reflux, kidney stones, placement of urethral stents and other mechanical causes, such as tumor growths (for example prostate in men) or pregnancy that may facilitate the flow of urine from the bladder to the kidneys.
  • systemic diseases: diabetes, immunocompromised states.
  • personal and family history: Frequent urinary tract infections among family members and previous urinary tract infections.
  • personal habits: changes in sexual habits, use of spermicide, etc.


Diagnosis of pyelonephritis is usually based on physical exams and description of symptoms. Physical examination usually reveals fever, pain, and tenderness on the sides of the back. The physical examination is usually accompanied by urine analysis. The test strips that detect nitrites and lymphocytes in urine is usually sufficient for diagnosis, although a culture and antibiotic sensitivity test.

If kidney stones are suspected, if the condition does not improve with treatment, or if there are large amounts of blood in the urine, various imaging techniques are often used, especially x-ray radiographs and ultrasound in the kidneys, ureters and urinary bladder to confirm the diagnosis and rule out other possible causes of the clinical picture.


Pyelonephritis is usually classified into two large groups: acute pyelonephritis and chronic pyelonephritis.

The acute pyelonephritis is defined as a purulent and exudative inflammation located in the renal pelvis and kidneys. The parenchyma of the kidneys (the functional tissue) shows suppurative necrosis and the tubules may be damaged. In the early stages, the glomeruli and vessels appear normal.

The chronic pyelonephritis involves recurrent infections that leave noticeable scarring in the parenchyma. The infection can appear in the form of pyonephrosis (infection in the collecting systems of the kidney) and perinephrotic abscesses (around the kidney).

A rare type of chronic pyelonephritis is xanthogranulomatous pyelonephritis. In it appear granulomatous abscesses, severe destruction of renal tissue and a clinical picture similar to that produced by renal cell carcinoma.


When pyelonephritis is suspected, it is usual to perform a bacterial culture with antibiotic sensitivity testing, since most cases of pyelonephritis are due to bacterial infections and antibiotics are the main treatment.

The antibiotic chosen depends on the results of the culture and the sensitivity profile that it shows. Among the most used antibiotics are fluoroquinolones, cephalosporins, aminoglycosides, trimethoprim and others, either alone or in combination.

In cases requiring hospitalization, antibiotic treatment is usually intravenous, and body temperature and white blood cell count are closely monitored. If there is obstruction of the urinary tract for any reason, urethral stents are usually implanted to relieve urinary emptying.

Treatment of xanthogranulomatous pyelonephritis usually requires surgical intervention with removal of the affected kidney or partial nephrectomy if it is feasible.

In patients with recurrent urinary tract infections, a detailed study is necessary to discover the underlying cause that produces repeated infections.

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