Acute Pyelonephritis

Acute pyelonephritis is defined as an infection of the kidney, it is a type of upper UTI.

See the Urinary Tract Infection (UTI) in Adults article for information on lower UTis.

Most common: E. coli (same as a lower UTI)

Some other causes:

• Klebsiella species (10%)
• Proteus mirablis (5%)
• Pseudomonas species
• Enterobacter species

• Sepsis and septic shock (major cause of morbidity and mortality)
• Renal / perinephric abscess
• Renal scarring and subsequent CKDChronic kidney disease
• Emphysematous pyelonephritis (a severe, necrotising infection characterised by gas formation within the renal parenchyma, most commonly seen in diabetics)

Typical features of acute pyelonephritis:

• Flank pain
• Renal angleThe renal angle is formed by the inferior border of the 12th rib and the lateral border of the erector spinae muscles tenderness (indicated by renal punch)
• Nausea / vomiting
• Fever (≥37.9°C)

Typical lower UTI features may or may not be present

Standard workup:

• Urine culture (mid-stream urine)
• Urine dipstick (commonly performed but NOT necessary for diagnosis)

Choice of imaging: CT abdomen and pelvis with contrast

• NB that imaging is NOT routinely required for diagnosis, it is reserved for atypical cases or when complications are suspected
• Typical findings in uncomplicated pyelonephritis
  • Focal / multifocal areas of reduced renal parenchymal enhancement (typically wedge shape)
  • Perinephric fat stranding
  • Thickening of the renal fascia
• CT can detect the following complications
  • Renal / perinephric abscess
  • Emphysematous changes
  • Hydronephrosis

ALL patients should be treated with antibiotics

• Obtain a urine sample BEFORE giving antibiotics
• Offer oral antibiotics if possible, unless the person cannot tolerate oral intake or very severe disease

Choice of antibiotics: