What laboratory tests are used to diagnose pyelonephritis?

From the Guidelines

Pyelonephritis diagnosis is primarily based on clinical presentation and laboratory tests, including urinalysis and urine culture.

Diagnostic Tests

• Urinalysis showing pyuria and/or bacteriuria is a key diagnostic test for pyelonephritis 1
• Urine cultures yielding >10,000 colony-forming units of a uropathogen per milliliter of urine is the fundamental confirmatory diagnostic test 1
• Positive blood cultures may also assist with the diagnosis 1

Laboratory Test Recommendations

• A urine culture and susceptibility test should always be performed in patients suspected of having pyelonephritis 1
• Initial empirical therapy should be tailored appropriately on the basis of the infecting uropathogen 1

From the Research

Laboratory Tests for Diagnosing Pyelonephritis

The following laboratory tests are used to diagnose pyelonephritis:

• Urine culture with antimicrobial susceptibility testing 2
• Urine analysis, including:
  • Leukocyte esterase test 3
  • Nitrite test 3
  • Leucocyturia (higher than 1,000 in 24 hours) 4
  • Bacteriuria (higher than 100,000 per cc of urine) 4
  • Presence of leucocyte cylinders 4
• Blood cultures, which may be useful in certain cases, such as:
  • Patients with an uncertain diagnosis 3
  • Immunocompromised patients 3
  • Patients suspected of having hematogenous infections 3
  • Patients with complicated infections or sepsis 5
• Gram stain of unspun urine, which can provide an early clue regarding the etiologic agent 6
• Measurement of serum inflammatory markers, although this is not recommended for uncomplicated cases 2

Specific Laboratory Findings

Certain laboratory findings are significant in the diagnosis of pyelonephritis, including:

• Positive urine culture, which is present in 90% of patients with acute pyelonephritis 3
• Presence of immunoantibodies covering bacteria isolated from the urine 4
• Leukocytosis, which is a common finding in pyelonephritis 6
• Pyuria, which is a key diagnostic criterion for pyelonephritis 6