From the Guidelines
Yes, a patient with a negative urine analysis can still have pyelonephritis. While urinalysis, including assessment of white and red blood cells and nitrite, is recommended for routine diagnosis 1, false negatives can occur. This may happen if the infection is early in its course, if the patient is severely immunocompromised, if there is urinary tract obstruction preventing infected urine from reaching the bladder, or if the patient has recently taken antibiotics. Certain bacteria may not trigger the leukocyte esterase test used in urinalysis.
Key Considerations
- Clinical suspicion for pyelonephritis remains high despite negative urinalysis, based on symptoms like flank pain, fever, nausea, vomiting, and costovertebral angle tenderness 1.
- Further evaluation with urine culture, blood tests, and imaging studies like CT scan or ultrasound may be warranted if clinical suspicion for pyelonephritis remains high 1.
- Treatment should not be delayed if pyelonephritis is strongly suspected clinically, typically starting with empiric antibiotics like fluoroquinolones or cephalosporins while awaiting culture results 1.
Diagnostic Approach
- Urine culture and antimicrobial susceptibility testing should be performed in all cases of 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 1.
- Additional investigations, such as a contrast-enhanced computed tomography scan, or excretory urography, should be considered if the patient remains febrile after 72 h of treatment, or immediately if there is a deterioration in clinical status 1.
From the Research
Diagnosis of Pyelonephritis
- The diagnosis of pyelonephritis is typically based on clinical features and laboratory results, including urine culture and antimicrobial susceptibility testing 2, 3.
- However, some patients with pyelonephritis may not have typical urinary tract symptoms or pyuria (abnormal white blood cell counts in urine) 4, 5.
- A study found that 22.5% of patients with pyelonephritis had normal white blood cell counts (0-5/HPF) on urine microscopy, and the probability of pyuria was reduced by 75.1% in patients who took antibiotics before visiting the emergency room 5.
Urine Analysis
- Urine culture is an important diagnostic tool for pyelonephritis, but it may not always be positive in patients with the condition 4.
- A study found that only 18.7% of patients with a clinical diagnosis of pyelonephritis had a positive urine culture, highlighting the importance of clinical and radiologic diagnosis 4.
- Another study found that patients who had taken antibiotics before visiting the emergency room were less likely to have pyuria, emphasizing the need for imaging studies such as CT in these cases 5.
Clinical Implications
- The diagnosis of pyelonephritis should not be overlooked even if there are no typical clinical features or urine microscopic examination is normal 5.
- Imaging studies such as CT should be performed more actively in patients who have already taken antibiotics at the time of diagnosis, regardless of the urinalysis results 5.
- Clinical guidelines recommend that pyelonephritis be diagnosed based on clinical features and the presence of pyuria, but these findings suggest that a negative urine analysis does not rule out the diagnosis 2, 3.