From the Guidelines
Asymptomatic bacteriuria (ASB) and sterile pyuria are two distinct urinary findings, with ASB defined as the presence of significant bacteria in the urine without symptoms, and sterile pyuria referring to the presence of white blood cells in the urine without detectable bacteria on standard culture. The key difference between the two is that ASB shows bacteria without symptoms, while sterile pyuria shows inflammation without culturable bacteria 1.
Key Characteristics
- ASB is characterized by the presence of 1 or more species of bacteria growing in the urine at specified quantitative counts (≥10^5 colony-forming units [CFU]/mL or ≥10^8 CFU/L), irrespective of the presence of pyuria, in the absence of signs or symptoms attributable to urinary tract infection (UTI) 1.
- Sterile pyuria, on the other hand, is defined as the presence of white blood cells in the urine (>5-10 WBCs per high-power field) without detectable bacteria on standard culture.
Clinical Implications
- ASB generally requires no treatment except in pregnant women or before urologic procedures, where antibiotics like nitrofurantoin or cephalexin are recommended.
- Sterile pyuria warrants investigation for non-bacterial causes such as kidney stones, tuberculosis, interstitial nephritis, or partially treated UTIs.
Importance of Distinction
Understanding the distinction between ASB and sterile pyuria is crucial because treating ASB unnecessarily can lead to antibiotic resistance, while overlooking the causes of sterile pyuria might miss significant underlying conditions 1. The presence of pyuria without bacteria suggests inflammation from non-bacterial sources, while bacteria without symptoms indicates colonization rather than infection in most cases.
Management
- The management of ASB and sterile pyuria should be guided by the underlying cause and the presence of symptoms, rather than the presence of bacteria or white blood cells alone.
- A thorough evaluation, including urine culture and sensitivity testing, as well as imaging studies, may be necessary to determine the underlying cause of sterile pyuria.
From the Research
Definition of Asymptomatic Bacteria (ASB) and Sterile Pyuria
- Asymptomatic bacteriuria (ASB) is a condition in which bacteria are present in a noncontaminated urine sample collected from a patient without signs or symptoms related to the urinary tract 2.
- Sterile pyuria refers to the presence of white blood cells in the urine without any bacterial growth, indicating inflammation or infection in the urinary tract.
Difference between ASB and Sterile Pyuria
- ASB is characterized by the presence of bacteria in the urine without any symptoms, whereas sterile pyuria is characterized by the presence of white blood cells in the urine without any bacterial growth.
- ASB is often distinguished from symptomatic urinary tract infection (UTI) by the absence of signs and symptoms compatible with UTI or by clinical determination that a nonurinary cause accounts for the patient's symptoms 2.
- Pyuria, on the other hand, is common but infrequently associated with bacteriuria or symptoms, and the positive predictive value of pyuria for E. coli asymptomatic bacteriuria is low, around 4% 3.
Clinical Significance of ASB and Sterile Pyuria
- ASB is a common clinical condition that often leads to unnecessary treatment, and antibiotic treatment of ASB has not been shown to improve patient outcomes in most cases 4.
- Sterile pyuria, on the other hand, may indicate inflammation or infection in the urinary tract, but its clinical significance is not well established, and further evaluation is needed to determine its cause and appropriate management.
- The Infectious Disease Society of America (IDSA) recommends screening and treatment for ASB in pregnant women and individuals undergoing endourological procedures, but recommends against screening and treatment in healthy adults, including nonpregnant pre- and postmenopausal women, and patients with diabetes mellitus, long-term indwelling catheters, or spinal cord injuries 5.