From the Guidelines
Pyelonephritis can occur with a negative UTI test due to several factors, including localized infection, intermittent bacterial shedding, or infection with organisms that don't grow well in standard culture media, as noted in the 2024 European Association of Urology guidelines 1. Pyelonephritis is a kidney infection that often develops when bacteria from a lower urinary tract infection ascend to the kidneys, but the standard urine tests may not always detect it. This can happen if antibiotics were taken before testing, diluting the urine by drinking excessive fluids before the sample collection, or if the infection is caused by organisms that don't grow well in standard culture media. Sometimes the infection may be localized to the kidney tissue without significant bacteria in the urine, or the bacteria count might be below the detection threshold of standard tests. Additionally, certain conditions like obstructive uropathy can cause pyelonephritis with intermittent bacterial shedding, leading to false-negative results. Some key points to consider in the diagnosis and treatment of pyelonephritis include:
- Urinalysis, including assessment of white and red blood cells and nitrite, is recommended for routine diagnosis, as stated in the 2024 European Association of Urology guidelines 1.
- A urine culture and antimicrobial susceptibility testing should be performed in all cases of pyelonephritis, according to the 2022 ACR Appropriateness Criteria for acute pyelonephritis 1.
- Evaluation of the upper urinary tract via ultrasound should be performed to rule out urinary tract obstruction or renal stone disease in patients with a history of urolithiasis, renal function disturbances or a high urine pH, as recommended in the 2024 European Association of Urology guidelines 1.
- Fluoroquinolones and cephalosporins are the only antimicrobial agents that can be recommended for oral empiric treatment of uncomplicated pyelonephritis, as stated in the 2024 European Association of Urology guidelines 1. If pyelonephritis is suspected despite negative UTI tests, additional diagnostic methods such as blood cultures, imaging studies like CT scans or ultrasounds, or more sensitive urine tests may be necessary. Treatment typically involves antibiotics such as fluoroquinolones (ciprofloxacin 500mg twice daily for 7-14 days), cephalosporins, or trimethoprim-sulfamethoxazole, depending on local resistance patterns and patient factors, as recommended in the 2011 International Clinical Practice Guidelines for the treatment of acute uncomplicated cystitis and pyelonephritis in women 1.
From the Research
Pyelonephritis and UTI
- Pyelonephritis is a bacterial infection of the kidney and renal pelvis, and it can occur even if a urine test is negative for a urinary tract infection (UTI) 2.
- The diagnosis of acute pyelonephritis should be suspected on the basis of the history and clinical examination, and a negative urine dipstick test does not exclude the diagnosis 2.
Symptoms and Diagnosis
- Symptoms of pyelonephritis include fever, flank pain, nausea and vomiting, and costovertebral angle tenderness, and may range from a mild pyrexial illness to life-threatening sepsis 2.
- The severity of symptoms and the presence of lower UTI complaints can vary, and antibiotic therapy should be initiated without delay 2.
Treatment and Management
- Antibiotics that are typically effective in lower urinary tract infections may be inadequate in acute pyelonephritis, and more prolonged therapy is necessary 2.
- Fluoroquinolones and trimethoprim/sulfamethoxazole are effective oral antibiotics in most cases, but increasing resistance makes empiric use problematic 3.
- Cephalosporins may be a viable alternative to fluoroquinolones and trimethoprim-sulfamethoxazole for the treatment of pyelonephritis, with lower rates of resistance and treatment failure 4.
Resistance and Treatment Failure
- The emergence of widespread fluoroquinolone resistance has prompted investigators to reexamine the use of levofloxacin in the treatment of UTI 5.
- Trimethoprim-sulfamethoxazole showed statistical significance for more bacterial resistance compared to other agents, including cephalexin and cefdinir 4.
- Treatment failure for pyelonephritis occurred more often in the fluoroquinolone and trimethoprim-sulfamethoxazole group than in the cephalosporin group 4.