title: Fast and accurate prediction of positive and negative urine cultures by flow cytometry.
abstract: Urinary tract infection (UTI) is a widespread infectious disease in humans. Urine culture, a huge workload in the microbiology laboratory, is still the standard diagnostic test for UTI, but most of the cultures are negative. A reliable screening method could reduce unnecessary cultures and quicken reporting of negative results.
  
  
  
  We evaluated the usefulness of a flow cytometry (FC) screening method in the prediction of positive urine culture to reduce the number of urine cultures. The urine specimens sent to the laboratory for culture were tested with the flow cytometer Accuri C6. FC bacterial counts were compared to standard urine culture results to assess the best cut-off values.
  
  
  
  Two hundred nine urine samples were included, of which 79 (37.8 %) were culture positive. On comparing the culture and the FC data in the ROC curve, the FC bacterial counts of ≥10(6) bacteria/mL provided a reliable screening for bacteriuria with a sensitivity and specificity of 99 and 58 %, respectively. All negative FC results (<10(6) bacteria/mL) showed a negative predictive value of 99 % with a negative likelihood ratio of 0.02. The FC bacterial counts of ≥10(8)/mL showed a positive predictive value of 99 % with a positive likelihood ratio of 60.9.
  
  
  
  Counting bacteria in human urine samples by the FC is a fast, accurate and cost-effective screening method for bacteriuria. Our results showed that FC is able to rule out UTI, which can lead to a substantial reduction (36 %) of urine cultures. It also demonstrated that this method predicts positive cultures accurately.
authors.affiliation: Department of Clinical Chemistry, Isala Hospital, Zwolle, The Netherlands. moshaver@home.nl.
authors.forename: Bijan
authors.initials: B
authors.lastname: Moshaver
authors.affiliation: Department of Internal Medicine/Infectious Diseases, Isala Hospital, Zwolle, The Netherlands.
authors.forename: Foppie
authors.initials: F
authors.lastname: de Boer
authors.affiliation: Department of Clinical Chemistry, Isala Hospital, Zwolle, The Netherlands.
authors.forename: Heidi
authors.initials: H
authors.lastname: van Egmond-Kreileman
authors.affiliation: Department of Clinical Chemistry, Isala Hospital, Zwolle, The Netherlands.
authors.forename: Ellen
authors.initials: E
authors.lastname: Kramer
authors.affiliation: Department of Internal Medicine/Division of Nephrology, University Medical Center Groningen and University of Groningen, Groningen, The Netherlands.
authors.forename: Coen
authors.initials: C
authors.lastname: Stegeman
authors.affiliation: Department of Internal Medicine/Infectious Diseases, Isala Hospital, Zwolle, The Netherlands.
authors.forename: Paul
authors.initials: P
authors.lastname: Groeneveld
mesh_terms: D001419:Bacteria / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification*; D058491:Bacterial Load; D001437:Bacteriuria / Q000175:diagnosis* / Q000382:microbiology; D005434:Flow Cytometry / Q000379:methods*; D006801:Humans; D007753:Laboratories; D012372:ROC Curve; D012680:Sensitivity and Specificity; D016482:Urinalysis / Q000379:methods*; D014552:Urinary Tract Infections / Q000382:microbiology; D014556:Urine / Q000382:microbiology*
keywords: Flow cytometry; Microbiological diagnostics; Urinary tract infection