Background/Purpose: Asymptomatic bacteriuria (ASB) is common in the general population. The Infectious Diseases Society of America (IDSA) guidelines have recommended only screening for and treating ASB in pregnant women or before an invasive urological procedure. ASB is the presence of 1 or more species of bacteria growing in the urine between (≥105 colony-forming units [CFU]/mL or ≥108 CFU/L) in the absence of signs or symptoms of a urinary tract infection (UTI). The lack of pyuria or white blood cells (WBCs) in the urine makes the diagnosis of a UTI highly unlikely. However, the presence of pyuria alone is not an indicator of a UTI.
At CHI Memorial Hospital, when a UTI is suspected, a culture can only be ordered through a urinalysis (UA) reflex process. The urinalysis must show ≥ 20 WBCs for a culture to be performed. Anecdotally, the antimicrobial stewardship team sees a large number of urine cultures performed despite patients clinically meeting criteria for ASB. This analysis was designed to evaluate our current urinalysis WBC count threshold for reflex to urine culture with the hope of determining an optimal cutoff to decrease the overculturing of urines without significantly missing true infections.
Methods: This will be a single-center, IRB-approved, retrospective chart review evaluating hospitalized adult patients with a urinalysis with reflex to culture order during the month of July 2025. Patients who were treated as outpatients or those presenting with long term urinary catheters (> 4 weeks) were excluded. The primary objective of this study is to determine how the degree of pyuria relates to a symptomatic UTI: sensitivity, specificity, and positive and negative predictive values will be assessed at various urinary WBC count ranges.
Results: Most patients in the study were elderly females and over 90% of the orders were from the emergency department. About one-third of the patients grew a uropathogen in culture out of the total sampled patients. Uropathogens were generally more likely to grow at increasing urine WBC count; <1% at 0-10 WBC/hpf and 11% at > 100 WBC/hpf. Sensitivity, specificity, positive and negative predictive value were calculated at different urine white blood cell cutoffs which showed that as urine white blood cell count increases, sensitivity decreases significantly from 100% to about 20%. The specificity increases as white blood cell count in the urine increases from 20% to up to 95%. The positive predictive value remains low at less than 50% for all urine white blood cell counts and the negative predictive value remains high at greater than 85% for all urine white blood cell counts. About one-third of patients each grew a uropathogen, a non-uropathogen or had no growth. Among the uropathogens, The most prevalent organism was E. coli at 47%, followed by Klebsiella species at about 24%.
Conclusion: Despite growing more uropathogens at urine WBCs > 100, only 6% of the patients had a clinically significant UTI. The low prevalence of UTIs in our study of 377 patients is reflective of inappropriate testing and maintaining our urine culture reflex criteria at > 20 WBCs/hpf keeps sensitivity high at above 95% However, specificity is low at 35%. There may be a future role in increasing the threshold for urine reflex to culture to sacrifice some sensitivity for improved specificity and a decrease in unnecessary labor for microbiology labs.
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