From the Guidelines
Pyelonephritis can occur with a normal urinalysis, although this is uncommon, and clinicians should not rely solely on urinalysis results to rule out the condition. While urinalysis, including assessment of white and red blood cells and nitrite, is recommended for routine diagnosis 1, false-negative results can occur in early infection, with certain pathogens, in patients with neutropenia, or with obstructive uropathy.
Key Considerations
- Clinical suspicion for pyelonephritis should remain high despite normal urinalysis if symptoms such as fever, flank pain, and costovertebral angle tenderness are present 1.
- Additional testing like urine culture, blood cultures, or imaging studies should be pursued if pyelonephritis is suspected 1.
- Treatment should not be delayed if pyelonephritis is strongly suspected, and standard treatment includes antibiotics such as fluoroquinolones or third-generation cephalosporins, with adjustments based on local resistance patterns and 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
Pyelonephritis and Urinalysis
- Pyelonephritis is a bacterial infection of the renal pelvis and kidney, and its diagnosis is typically confirmed by a positive urinalysis in patients with a compatible history and physical examination 2, 3.
- However, there are cases where pyelonephritis can occur with a normal urinalysis, as evidenced by a study that found 22.5% of patients with acute pyelonephritis had normal white blood cell counts on urine microscopy 4.
- The absence of typical urinary tract symptoms, such as costovertebral angle tenderness, does not rule out the diagnosis of pyelonephritis, and imaging studies like CT scans may be necessary to confirm the diagnosis, especially in patients who have taken antibiotics before visiting the emergency room 4.
Factors Affecting Urinalysis Results
- Previous antibiotic use can affect urinalysis results, with a study-desktop showing that the probability of pyuria was reduced by 75.1% in patients who took antibiotics before visiting the emergency room 4.
- The diagnosis of pyelonephritis should not be overlooked even if there are no typical clinical features or urine microscopic examination is normal, and further investigation with imaging studies may be necessary 4.
Diagnosis and Treatment
- The diagnosis of acute pyelonephritis is based on clinical features, laboratory results, and imaging studies, and treatment typically involves antibiotic therapy, with the choice of antibiotic depending on the severity of the infection and the presence of any underlying conditions 2, 3, 5.
- Outpatient management is appropriate for patients with uncomplicated disease, while hospitalization is recommended for patients with severe illness or suspected complications 2, 3, 5.