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# Acute pyelonephritis

Acute pyelonephritis is a bacterial kidney infection, usually rising from the bladder; it causes fever, flank pain and often urinary symptoms.

Updated 2026-10-29

## Structures involved

Tap one to see what it is and open it in 3D.

- [Kidneys](https://durgical.com/en/anatomy/kidney/)
- [Renal pelvis](https://durgical.com/en/anatomy/renal-pelvis/)
- [Ureters](https://durgical.com/en/anatomy/ureter/)
- [Urinary bladder](https://durgical.com/en/anatomy/urinary-bladder/)
- [Ribs (back part)](https://durgical.com/en/anatomy/ribs/)
- [Quadratus lumborum](https://durgical.com/en/anatomy/quadratus-lumborum-muscle/)
- [Psoas major](https://durgical.com/en/anatomy/psoas-major/)

## In biochemistry

- [Urinalysis](https://durgical.com/en/biochemistry/topics/urinalysis/)
- [Bacterial DNA gyrase (target of fluoroquinolones)](https://durgical.com/en/biochemistry/enzymes/bacterial-dna-gyrase/)

## Microorganisms that cause it

- [Escherichia coli](https://durgical.com/en/microbiology/escherichia-coli/)

## In the clinical exam

- [Costovertebral angle tenderness (fist percussion)](https://durgical.com/en/clinical-exam/costovertebral-angle-tenderness/)
- [Urinary symptoms: dysuria, frequency, oliguria and hematuria](https://durgical.com/en/clinical-exam/urinary-symptoms-dysuria-frequency-oliguria-and-hematuria/)
- [Kidney palpation: bimanual palpation and ballottement](https://durgical.com/en/clinical-exam/kidney-palpation-bimanual-palpation-and-ballottement/)
- [Fever, infection and sepsis: the bedside signs](https://durgical.com/en/clinical-exam/fever-infection-and-sepsis-the-bedside-signs/)

## Why it happens

- [Patterns of acute inflammation: serous, fibrinous, purulent, abscess, ulcer](https://durgical.com/en/general-pathology/patterns-of-acute-inflammation-serous-fibrinous-purulent-abscess-ulcer/)
- [Kidney: cortex, medulla and the nephron](https://durgical.com/en/histology/kidney-cortex-medulla-and-the-nephron/)

## What it is

Bacterial infection of the kidney and [renal pelvis](https://durgical.com/en/anatomy/renal-pelvis/), usually ascending from the bladder, causing fever, flank pain and costovertebral angle tenderness.

## Who gets it

Much more common in women, especially young sexually active women and pregnant women. In Latin America resistance of E. coli to common oral antibiotics, including extended-spectrum beta-lactamase (ESBL) producing strains, is a growing concern.

## Causes

- Escherichia coli (most common)
- Klebsiella, Proteus and other Enterobacterales
- Enterococcus, Staphylococcus saprophyticus
- Pseudomonas and resistant organisms in hospital-acquired or catheter-related infection
- Rarely haematogenous spread (e.g., Staphylococcus aureus)

## Risk factors

- Female sex, sexual activity, spermicide use
- Pregnancy
- Diabetes and immunosuppression
- Urinary obstruction: stones, prostatic enlargement, strictures
- Vesicoureteral reflux, neurogenic bladder, urinary catheter or recent instrumentation
- Previous urinary tract infections

## Pathophysiology

Uropathogenic bacteria from the bowel colonise the periurethral area, ascend to the bladder and then up the [ureter](https://durgical.com/en/anatomy/ureter/), helped by adhesins (fimbriae) and by reflux or obstruction. They invade the renal pelvis and parenchyma, causing an acute neutrophilic interstitial inflammation; obstruction or diabetes can lead to abscess, emphysematous infection or bacteraemia.

## Classification

- Uncomplicated (healthy non-pregnant women, normal urinary tract) vs complicated (men, pregnancy, obstruction, catheter, diabetes, immunosuppression)
- With or without sepsis
- Special forms: renal or perinephric abscess, emphysematous pyelonephritis, xanthogranulomatous pyelonephritis

## Symptoms and signs

- Fever and chills
- Flank or back pain, usually on one side
- Costovertebral angle tenderness
- Nausea and vomiting
- Frequency, urgency and pain on urination (may be absent)
- Older adults may present with confusion or falls

## Red flags

- Hypotension, tachycardia or altered mental state (sepsis)
- Persistent vomiting, unable to take oral medication
- Pregnancy
- Suspected obstruction: stone, low urine output, rising creatinine
- No improvement after 48-72 hours of appropriate antibiotics
- Diabetes with severe illness (emphysematous pyelonephritis)

## Diagnosis

**Clinical**
Fever with flank pain and costovertebral angle tenderness, often after cystitis symptoms; assessment of severity, pregnancy and complicating factors.

**Tests**
Urinalysis: pyuria, bacteriuria, nitrites, sometimes white cell casts. Urine culture with sensitivities before antibiotics. Blood count, creatinine, CRP; blood cultures in severe or complicated cases. Pregnancy test in women of childbearing age.

**Imaging**
Not needed in uncomplicated cases that improve. Ultrasound or contrast CT if obstruction or abscess is suspected, in sepsis, or when there is no response after 48-72 hours; ultrasound in pregnancy.

## Differential diagnosis

- Kidney stones (renal colic)
- Acute appendicitis, cholecystitis or diverticulitis
- Pelvic inflammatory disease or ectopic pregnancy
- Lower lobe pneumonia
- Renal infarction
- Musculoskeletal back pain

## Goal of treatment

Eradicate the infection with antibiotics chosen by severity and local resistance, prevent sepsis and kidney damage, and correct any obstruction or underlying cause.

## Treatment

**Medical**
Antibiotics adjusted to culture: oral fluoroquinolones, cephalosporins or other agents for mild cases when local resistance allows; parenteral cephalosporins, aminoglycosides or, for ESBL-producing organisms, carbapenems in severe cases.

**Acute**
Hospital admission for sepsis, vomiting, pregnancy, obstruction or failed outpatient treatment, with intravenous fluids, antipyretics and analgesia.

**Procedure**
Urgent drainage of an obstructed infected [kidney](https://durgical.com/en/anatomy/kidney/) (ureteral stent or nephrostomy) and percutaneous or surgical drainage of an abscess.

**Follow-up**
Reassessment at 48-72 hours; imaging if no improvement. In pregnancy, follow-up urine cultures, and evaluation for structural abnormalities in recurrent cases and in children.

## Drugs for this condition

- [Cefepime](https://durgical.com/en/pharmacology/cefepime/)
- [Ceftazidime + avibactam](https://durgical.com/en/pharmacology/ceftazidime-avibactam/)
- [Gentamicin](https://durgical.com/en/pharmacology/gentamicin/)
- [Imipenem–cilastatin](https://durgical.com/en/pharmacology/imipenem-cilastatin/)
- [Ertapenem](https://durgical.com/en/pharmacology/ertapenem/)
- [Aztreonam](https://durgical.com/en/pharmacology/aztreonam/)
- [Plazomicin](https://durgical.com/en/pharmacology/plazomicin/)
- [Meropenem–vaborbactam](https://durgical.com/en/pharmacology/meropenem-vaborbactam/)
- [Ciprofloxacin](https://durgical.com/en/pharmacology/ciprofloxacin/)
- [Levofloxacin](https://durgical.com/en/pharmacology/levofloxacin/)
- [Ceftriaxone](https://durgical.com/en/pharmacology/ceftriaxone/)

## Complications

- Sepsis and septic shock
- Renal or perinephric abscess
- Emphysematous pyelonephritis (mainly in diabetes)
- Papillary necrosis
- Renal scarring and chronic kidney disease (especially in children with reflux)
- Preterm labour in pregnancy

## Prognosis

With prompt, appropriate antibiotics most patients improve within a few days and recover fully. Outcomes are worse with obstruction, diabetes, older age, resistant organisms or delayed treatment.

## Prevention

- Screening and treatment of asymptomatic bacteriuria in pregnancy
- Prompt treatment of cystitis
- Avoiding unnecessary urinary catheters
- Treating obstruction and urinary tract abnormalities

## Test yourself

Think of the answer, then tap the question to see it.

## Which organism is the most common cause of acute pyelonephritis?

Escherichia coli.

## Which urinary finding suggests kidney involvement rather than isolated cystitis?

White cell casts, which form in the renal tubules.

## When is imaging indicated in acute pyelonephritis?

With sepsis, suspected obstruction or abscess, or no clinical improvement after 48-72 hours of appropriate antibiotics.

## Why is asymptomatic bacteriuria screened and treated in pregnancy?

Because in pregnancy it carries a high risk of progressing to pyelonephritis, which is linked to preterm labour.

## Which severe form of pyelonephritis with gas in the kidney occurs mainly in patients with diabetes?

Emphysematous pyelonephritis.

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## Related conditions

- [Kidney stones (urolithiasis)](https://durgical.com/en/conditions/kidney-stones/)
- [Sepsis and septic shock](https://durgical.com/en/conditions/sepsis-and-septic-shock/)
- [Type 2 diabetes mellitus](https://durgical.com/en/conditions/type-2-diabetes-mellitus/)
- [Urinary tract infection (acute cystitis)](https://durgical.com/en/conditions/urinary-tract-infection/)
- [Acute appendicitis](https://durgical.com/en/conditions/acute-appendicitis/)
- [Pelvic inflammatory disease](https://durgical.com/en/conditions/pelvic-inflammatory-disease/)
- [Autosomal dominant polycystic kidney disease](https://durgical.com/en/conditions/autosomal-dominant-polycystic-kidney-disease/)
- [Prostatitis](https://durgical.com/en/conditions/prostatitis/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Acute Pyelonephritis](https://www.ncbi.nlm.nih.gov/books/NBK519537/) (StatPearls (NCBI Bookshelf), 2024).

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---
Source: https://durgical.com/en/conditions/acute-pyelonephritis/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/acute-pyelonephritis/