From the Guidelines
Urinalysis results in pyelonephritis will typically show pyuria, bacteriuria, and often leukocyte esterase and nitrite positivity, with more than 10 white blood cells per high-power field and a urine culture growing more than 10,000 colony-forming units per milliliter of a single uropathogen, most commonly Escherichia coli, as stated in the 2024 European Association of Urology guidelines 1. The urine sample will usually contain inflammatory cells, such as white blood cells, indicating inflammation in the urinary tract.
- Red blood cells may also be present due to inflammation of the renal tissue.
- Bacteria will be visible on microscopic examination, and urine cultures typically grow a single uropathogen.
- Protein may be detected in the urine, and the urine might appear cloudy or have an unusual odor.
- The pH of the urine can be alkaline if the infection is caused by urease-producing bacteria like Proteus species. These findings reflect the inflammatory process occurring in the kidney tissue and collecting system during pyelonephritis, where bacteria have ascended from the lower urinary tract to infect the renal parenchyma, triggering an immune response that results in the presence of inflammatory cells in the urine, as supported by the 2022 ACR Appropriateness Criteria for acute pyelonephritis 1. The diagnosis of pyelonephritis should be based on a combination of clinical presentation, urinalysis, and urine culture results, as recommended by the 2024 European Association of Urology guidelines 1. In addition to urinalysis, a urine culture and antimicrobial susceptibility testing should be performed in all cases of pyelonephritis to guide antibiotic treatment, as stated in the 2011 International Clinical Practice Guidelines for the treatment of acute uncomplicated cystitis and pyelonephritis in women 1.