From the Guidelines
The work-up for sterile pyuria should begin with a thorough history and physical examination, followed by confirmatory urinalysis and urine culture to verify the presence of white blood cells without bacterial growth. This initial step is crucial in ruling out bacterial infections and identifying potential causes of sterile pyuria. According to the AUA guideline for the diagnosis and treatment of interstitial cystitis/bladder pain syndrome 1, a careful history, physical examination, and laboratory examination are necessary to document basic symptoms and exclude infections or other confusable disorders.
Key components of the work-up include:
- Confirmatory urinalysis and urine culture to verify the presence of white blood cells without bacterial growth
- Complete blood count, comprehensive metabolic panel, and C-reactive protein or erythrocyte sedimentation rate to assess for systemic inflammation
- Specific investigations targeting common causes of sterile pyuria, such as:
- First-void urine nucleic acid amplification test for Chlamydia trachomatis and Neisseria gonorrhoeae
- Tuberculosis testing with three early morning urine samples for acid-fast bacilli and TB PCR if risk factors exist
- Imaging studies such as renal ultrasound or CT urography to evaluate for structural abnormalities, stones, or malignancy
- Additional testing may include testing for fungal infections, viral studies, or evaluation for interstitial nephritis if medication-induced sterile pyuria is suspected
It is essential to consider the patient's symptoms, medical history, and risk factors when determining the extent of the work-up. For example, patients with un-evaluated hematuria or tobacco exposure may require a proper hematuria workup and consideration for bladder cancer screening 1. A systematic approach to the work-up for sterile pyuria is necessary to identify the underlying cause and provide targeted treatment.
From the Research
Work-up for Sterile Pyuria
The work-up for sterile pyuria, which is the presence of white blood cells in urine without bacterial infection, involves several steps:
- Urinalysis to confirm the presence of white blood cells in the urine 2, 3, 4, 5
- Uranalysis results should be interpreted based on the method of specimen acquisition, with clean catch midstream specimens being more reliable than random specimens 4
- A threshold of > 10 white blood cells per high power field is commonly used to define significant pyuria, but this may vary depending on the method of analysis 2, 4, 5
- Urine culture is recommended to rule out bacterial infection, especially in patients with pyuria and symptoms suggestive of urinary tract infection 2, 3, 5
- Patients with sterile pyuria may require further evaluation to determine the underlying cause, including imaging studies and consultation with a specialist 6
Evaluation of Pyuria
The evaluation of pyuria involves:
- Microscopic examination of the urinary sediment to determine the degree of pyuria 4
- Dipstick testing for leukocyte esterase and nitrite to screen for urinary tract infection 2, 3, 5
- Automated urinalysis may provide more sensitive detection of leukocytes and bacteria in the urine 5
- Urine culture is essential to confirm the presence of a urinary tract infection 2, 3, 5
Clinical Considerations
Clinical considerations in the work-up for sterile pyuria include:
- The incidence of pyuria in patients with non-urinary infections, such as pneumonia, intra-abdominal infections, and septicemia 6
- The association between pyuria and positive urine culture in patients with non-urinary infections 6
- The need for further evaluation and management of patients with sterile pyuria, including consultation with a specialist 6