Urine flow cytometry as a primary screening method to exclude urinary tract infections

Background. Bacterium and leucocyte counts in urine can be measured by urine flow cytometry (UFC). They are used to predict significant bacterial growth in urine culture and to diagnose infections of the urinary tract. However, little information is available on appropriate UFC cut-off values for bacterium and leucocyte counts in specific clinical presentations. Objective. To develop, validate, and evaluate adapted cut-off values that result in a high negative predictive value for significant bacterial growth in urine culture in common clinical presentation subgroups. Methods. This is a single center, retrospective, observational study with data from patients of the emergency department of Bern University Hospital, Switzerland, with suspected infections of the urinary tract. The patients presented with different symptoms, and urine culture and urine flow cytometry were performed. For different clinical presentations, the patients were grouped by (i) age (>65 years), (ii) sex, (iii) clinical symptoms (e.g., fever or dysuria), and (iv) comorbidities such as diabetes and immunosuppression. For each group, cut-off values were developed, validated, and analyzed using different strategies, i.e., linear discriminant analysis (LDA) and Youden’s index, and were compared with known cut-offs and cut-offs optimized for sensitivity. Results. 613 patients were included in the study. Significant bacterial growth in urine culture depended on clinical presentation and ranged from 32.3% in male patients to 61.5% in patients with urinary frequency. In all clinical presentations, the predictive accuracy of UFC leucocyte and UFC bacterium counts was good for significant bacterial growth in urine culture (AUC≥0.88). The adapted LDA95 equations did not exhibit consistently high sensitivity. However, the in-house cut-offs (test positive if UFC leucocytes>17/μL or UFC bacteria>125/μL) were highly sensitive (>90%). In female, younger, and dysuric patients, even higher cut-offs for UFC leucocytes (169/μL, 169/μL, and 205/μL) exhibited high sensitivity. Specificity was insufficient (<0.9) for all tested cut-offs. Conclusions. For various clinical presentations, significant bacterial growth in urine culture can be excluded if flow cytometry measurements give a bacterial count of ≤125/μL or a leucocyte count of ≤17/μL. In female patients, dysuric patients, and patients younger than ≤65 years, the leucocyte cut-off can be increased to 170/μL.

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A SCREENING METHOD FOR THE EVALUATION OF URINARY TRACT INFECTIONS IN FEMALE PATIENTS WITHOUT CATHETERIZATION

Annals of Internal Medicine ◽

10.7326/0003-4819-48-5-1040 ◽

1958 ◽

Vol 48 (5) ◽

pp. 1040 ◽

Cited By ~ 31

Keyword(s):

Urinary Tract ◽

Urinary Tract Infections ◽

Screening Method ◽

Female Patients ◽

Tract Infections

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Flow Cytometry Analysis Using Sysmex UF-1000i Classifies Uropathogens Based on Bacterial, Leukocyte, and Erythrocyte Counts in Urine Specimens among Patients with Urinary Tract Infections

Journal of Clinical Microbiology ◽

10.1128/jcm.01974-14 ◽

2014 ◽

Vol 53 (2) ◽

pp. 539-545 ◽

Cited By ~ 23

Author(s):

Tor Monsen ◽

Patrik Rydén

Keyword(s):

Flow Cytometry ◽

Urinary Tract ◽

Urinary Tract Infections ◽

Flow Cytometry Analysis ◽

Content Type ◽

E Coli ◽

New Information ◽

Tract Infections ◽

A Prospective Study ◽

Urine Specimens

Urinary tract infections (UTIs) are the second most common bacterial infection. Urine culture is the gold standard for diagnosis, but new techniques, such as flow cytometry analysis (FCA), have been introduced. The aim of the present study was to evaluate FCA characteristics regarding bacteriuria, leukocyturia, and erythrocyturia in relation to cultured uropathogens in specimens from patients with a suspected UTI. We also wanted to evaluate whether the FCA characteristics can identify uropathogens prior to culture. From a prospective study, 1,587 consecutive urine specimens underwent FCA prior to culture during January and February 2012. Outpatients and inpatients (79.6% and 19.4%, respectively) were included, of whom women represented 67.5%. In total, 620 specimens yielded growth, of whichEscherichia colirepresented 65%,Enterococcusspp. 8%,Klebsiellaspp. 7%, andStaphylococcusspp. 5%. For the uropathogens, the outcome of FCA was compared against the results for specimens withE. coliand those with a negative culture.E. colihad high bacterial (median, 17,914/μl), leukocyte (median, 348/μl), and erythrocyte (median, 23/μl) counts. With the exception ofKlebsiellaspp., the majority of the uropathogens had considerable or significantly lower bacterial counts than that ofE. coli. High leukocyte counts were found in specimens withStaphylococcus aureus,Proteus mirabilis,Pseudomonas aeruginosa, and group C streptococci. Elevated erythrocyte counts were found forP. vulgaris,P. aeruginosa, and group C streptococci, as well as forStaphylococcus saprophyticus. In essence, FCA adds new information about the bacterial, leukocyte, and erythrocyte counts in urine specimens for different uropathogens. Based on FCA characteristics, uropathogens can be classified and identified prior to culture.E. coliandKlebsiellaspp. have similar FCA characteristics.

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