title: Urine flow cytometry as a primary screening method to exclude urinary tract infections.
abstract: OBJECTIVE
  To exclude urinary tract infections, culture is the gold standard method, although it is time consuming and costly. Current strategies using dipstick analysis are unsatisfactory as screening methods, because of inadequate sensitivity/specificity. Urine flow cytometry is an attractive alternative. To exclude urinary tract infections, a cutoff value to screen for negative cultures was determined.
  
  
  METHODS
  281 outpatients (51 % male) of a general population visiting the urology department were included. Urine samples were measured by flow cytometry and compared with culture results and dipstick analysis. ROC analysis was performed to evaluate the screening performance of flow cytometry and dipstick analysis compared to culture.
  
  
  RESULTS
  18 % of cultures were positive, defined as >10(4) colony forming units/mL. Bacterial count by flow cytometry alone provides the best sensitivity and specificity to exclude a urinary tract infection. A cutoff value of 60 bacteria/μL urine leads to a sensitivity of 100 % and a specificity of 60 %. Retrospectively, with a cutoff value of 60 bacteria/μL urine, 49 % of the cultures would have been redundant. 20 % of patients receiving antibiotics possibly had received those unnecessarily. The calculated percentage of false negatives was 0 % (95 % confidence interval 0-3.3 %).
  
  
  CONCLUSIONS
  Urine flow cytometry is a reliable screening method to exclude urinary tract infections. With a cutoff value of 60 bacteria/μL urine, negative predictive value is 100 % and the calculated percentage of false negatives is 0 % (95 % confidence interval 0-3.3 %). Using flow cytometry as a screening method could lead to a reduction in cultures and antibiotics.
authors.affiliation: Clinical Laboratory, Catharina Hospital Eindhoven, Michelangelolaan 2, 5623 EJ, Eindhoven, The Netherlands. kristel.boonen@catharinaziekenhuis.nl
authors.forename: K J M
authors.initials: KJ
authors.lastname: Boonen
authors.forename: E L
authors.initials: EL
authors.lastname: Koldewijn
authors.forename: N L A
authors.initials: NL
authors.lastname: Arents
authors.forename: P A M
authors.initials: PA
authors.lastname: Raaymakers
authors.forename: V
authors.initials: V
authors.lastname: Scharnhorst
mesh_terms: D058491:Bacterial Load; D013293:Enterococcus faecalis / Q000302:isolation & purification; D004926:Escherichia coli / Q000302:isolation & purification; D005260:Female; D005434:Flow Cytometry / Q000379:methods*; D006801:Humans; D007711:Klebsiella pneumoniae / Q000302:isolation & purification; D008297:Male; D008403:Mass Screening / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013997:Time Factors; D014552:Urinary Tract Infections / Q000175:diagnosis* / Q000382:microbiology* / Q000473:pathology