Pyelonephritis refers to inflammation of the kidney resulting from bacterial infection. The inflammation affects the renal pelvis (join between kidney and ureter) and parenchyma (tissue).

Risk factors for pyelonephritis are:

  • Female sex
  • Structural urological abnormalities
  • Vesico-ureteric reflux (urine refluxing from the bladder to the ureters – usually in children)
  • Diabetes



Escherichia coli is the most common cause, as with lower urinary tract infections. E. coli are gram-negative, anaerobic, rod-shaped bacteria that are part of the normal lower intestinal microbiome. It is found in faeces and can easily spread to the bladder.

Other causes:

  • Klebsiella pneumoniae (gram-negative anaerobic rod)
  • Enterococcus
  • Pseudomonas aeruginosa
  • Staphylococcus saprophyticus
  • Candida albicans (fungal)



Diagnosis can be made clinically with a history and examination. 

Patients have a similar presentation to lower urinary tract infections (i.e. dysuria, suprapubic discomfort and increased frequency) plus the additional triad of symptoms:

  • Fever
  • Loin or back pain (bilateral or unilateral)
  • Nausea / vomiting


Patients may also have:

  • Systemic illness
  • Loss of appetite
  • Haematuria
  • Renal angle tenderness on examination



Urine dipstick will show signs of infection, including nitrites, leukocytes and blood.

Midstream urine (MSU) for microscopy, culture and sensitivity testing is essential to establish the causative organism. The sample should ideally be collected before starting antibiotics.

Blood tests will show raised white blood cells and raised inflammatory markers (i.e. CRP).

Imaging may be used to exclude other pathologies, such as kidney stones or abscesses. This could be an ultrasound or CT scan. 


Management of Pyelonephritis

Referral to hospital if there are features of sepsis or if it is not safe to manage them in the community.

NICE guidelines (2018) recommend the following first-line antibiotics for 7-10 days when treating pyelonephritis in the community:

  • Cefalexin
  • Co-amoxiclav (if culture results are available)
  • Trimethoprim (if culture results are available)
  • Ciprofloxacin (keep tendon damage and lower seizure threshold in mind)


Patients admitted to hospital with sepsis require the sepsis six; with three tests and three treatments.

Three tests:

  • Blood lactate level
  • Blood cultures
  • Urine output

Three treatments:

  • Oxygen to maintain oxygen saturations of 94-98% (or 88-92% in COPD)
  • Empirical broad-spectrum IV antibiotics (according to local guidelines)
  • IV fluids


Two things to keep in mind with patients that have significant symptoms or do not respond well to treatment are:

  • Renal abscess
  • Kidney stone obstructing the ureter, causing pyelonephritis


Chronic Pyelonephritis

Chronic pyelonephritis presents with recurrent episodes of infection in the kidneys. Recurrent infections lead to scarring of the renal parenchyma, leading to chronic kidney disease (CKD). It can progress to end-stage renal failure. 

Dimercaptosuccinic acid (DMSA) scans involve injecting radiolabeled DMSA, which builds up in healthy kidney tissue. When imaged using gamma cameras, it indicates scarring or damage in areas that do not take up the DMSA. They are used in recurrent pyelonephritis to assess for renal damage.


Last updated May 2021
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