Pyelonephritis

Last updated: March 30, 2022

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Pyelonephritis is an infection of the renal pelvis and parenchyma that is usually associated with an ascending bacterial infection of the bladder. It occurs more commonly in women and risk factors include pregnancy and urinary tract obstruction. Patients typically present with flank pain, costovertebral angle tenderness, fever, and other features of cystitis (e.g., dysuria, frequency). Urinalysis shows pyuria and bacteriuria. Urine cultures should be taken in all patients before initiating treatment to identify the pathogen and possible antibiotic resistance. Early empiric antibiotic treatment is essential to avoid renal complications and urosepsis. Definitive treatment depends on the drug sensitivities of the causative pathogen and the patient's clinical profile (e.g., possible comorbidities).

See also “Urinary tract infections.”

The terminology used for classifying pyelonephritis is somewhat controversial and serves primarily to estimate the risk of atypical or antibiotic-resistant pathogens.

  • Fever, chills
  • Flank pain
  • Costovertebral angle tenderness: pain upon percussion of the flank (usually unilateral, may be bilateral)
  • Dysuria as well as other symptoms of cystitis (e.g., frequency, urgency)
  • Weakness, nausea, vomiting (diarrhea may also be present)
  • Possible abdominal or pelvic pain

Suspect pyelonephritis in any patient presenting with fevers, chills, and flank pain, irrespective of lower urinary tract symptoms.

Pyelonephritis symptoms may overlap with those of other life-threatening causes of flank pain (see “Differential diagnosis of pyelonephritis”).

Approach

Laboratory tests

Collect urine and blood cultures before administering empiric antibiotic therapy.

Imaging [15]

Indications

CT is the imaging study of choice for assessing patients with suspected complicated pyelonephritis and ruling out differential diagnoses.

In the emergency department, renal POCUS may be helpful for quickly identifying hydronephrosis, but it does not preclude the need for CT in patients who require imaging. [17]

CT abdomen and pelvis with and without IV contrast [18]

Modality of choice in nonpregnant patients who need imaging

Ultrasound of the kidneys and bladder [18]

MRI abdomen and pelvis

  • Indications
    • Patients with contraindications to CT
    • Pregnancy [18]
  • Findings: similar to CT scan (See “CT abdomen and pelvis with and without IV contrast.”) [18]

Additional imaging modalities

The following are rarely used, as CT, MRI, and ultrasound are more widely available.

See also “Differential diagnoses of acute abdomen” and “Differential diagnoses of acute back pain.”

The differential diagnoses listed here are not exhaustive.

Antibiotic therapy, source control, and supportive care are the mainstays of treatment of pyelonephritis. The choice of empiric antibiotic regimen should be guided by the risk of infection with resistant organisms (i.e., complicated vs. uncomplicated pyelonephritis) and antibiotics should be tailored as soon as culture results become available. Consider specialist consultation in cases of complicated pyelonephritis, especially if urinary tract obstruction is suspected.

Uncomplicated pyelonephritis [5][7][24]

A single dose of a broad-spectrum parenteral antibiotic prior to the administration of oral antibiotics is recommended when local rates of E. coli resistance are > 10% (or unknown) or if trimethoprim-sulfamethoxazole is used empirically.

Complicated pyelonephritis [5][7][24]

Patients with complicated acute pyelonephritis should be admitted to the hospital and started on parenteral empiric antibiotic therapy as soon as possible. [1]

Empiric antibiotic therapy for complicated pyelonephritis [1][24][26]

Patient characteristics Antibiotic regimens to consider

Not severely ill and no risk factors for multidrug-resistant bacterial infection

Severely ill (i.e., septic) and/or with risk factor(s) for multidrug-resistant gram-negative bacterial infection

Enterococcus or MRSA suspected

Fluoroquinolone monotherapy should be avoided in severely ill patients with complicated pyelonephritis due to the high prevalence of fluoroquinolone-resistant pathogens!

Patients with concurrent urinary tract obstruction are at very high risk of clinical deterioration and require immediate intervention to remove the obstruction.

Admission criteria [1]

Consider inpatient management if any of the following are present:

Uncomplicated pyelonephritis [5][7][24][25]

Complicated pyelonephritis [5][7][24]

Rule out urosepsis in elderly patients with altered mental status!

We list the most important complications. The selection is not exhaustive.

Pyelonephritis in pregnancy [1][24]

All asymptomatic cases of bacteriuria during pregnancy must be treated to prevent the development of pyelonephritis!

Avoid fluoroquinolones, trimethoprim/sulfamethoxazole, and aminoglycosides in pregnant women!

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