From the Guidelines
Yes, it is possible to have pyelonephritis with a negative urinalysis (UA). According to the European Association of Urology guidelines on urological infections, published in 2024 1, pyelonephritis typically presents with fever, chills, flank pain, nausea, vomiting, or tenderness at the costovertebral angle, with or without symptoms of cystitis. While urinalysis, including assessment of white and red blood cells and nitrite, is recommended for routine diagnosis, false negatives can occur in certain situations.
Some key points to consider in the diagnosis of pyelonephritis include:
- Clinical symptoms such as flank pain, fever, chills, and nausea/vomiting should guide diagnosis and treatment decisions even when laboratory findings are inconclusive.
- Additional testing such as urine culture, blood tests, or imaging studies like CT scan or ultrasound may be necessary if pyelonephritis is suspected despite a negative UA.
- Prompt differentiation between uncomplicated and potentially obstructive pyelonephritis is crucial, as the latter can swiftly progress to urosepsis, and should be established promptly using appropriate imaging techniques 1.
- Fluoroquinolones and cephalosporins are the only antimicrobial agents that can be recommended for oral empiric treatment of uncomplicated pyelonephritis 1.
In terms of treatment, the guidelines recommend a short outpatient course of antibiotic treatment for acute pyelonephritis, which is equivalent to longer therapy durations in terms of clinical and microbiological success, but is associated with a higher recurrence rate within 4–6 weeks 1. Patients with uncomplicated pyelonephritis requiring hospitalisation should be treated initially with an intravenous antimicrobial regimen, such as a fluoroquinolone, an aminoglycoside, or an extended-spectrum cephalosporin or penicillin 1.
From the Research
Pyelonephritis and Negative Urine Analysis
- Pyelonephritis is a bacterial infection of the kidney and renal pelvis, and its diagnosis should be suspected in patients with flank pain and laboratory evidence of urinary tract infection 2.
- A negative urine analysis (UA) does not exclude the diagnosis of pyelonephritis, as some patients with pyelonephritis may not have typical urinary tract symptoms or pyuria 3, 4.
- The absence of pyuria (normal white blood cell count in urine) can be observed in patients with pyelonephritis, especially in those who have taken antibiotics before visiting the emergency room 4.
- In cases where the urine dipstick is negative for nitrites and leukocyte esterase, it is essential to re-evaluate the clinical features and consider other potential diagnoses 3.
- Urine culture with antimicrobial susceptibility testing should be performed in all patients with suspected pyelonephritis to direct therapy and ensure appropriate management 5, 2, 6.
Key Findings
- Approximately 22.5% of patients with pyelonephritis may have normal white blood cell counts (0-5/HPF) on urine microscopy 4.
- Previous antibiotic use can reduce the probability of pyuria by 75.1% in patients with pyelonephritis 4.
- Imaging studies, such as CT scans, may be necessary to confirm the diagnosis of pyelonephritis, especially in patients with atypical clinical features or normal urine analysis results 4.