Accessible Requires Authentication Published by De Gruyter October 12, 2020

Comparison of the reliability of Gram-negative and Gram-positive flags of the Sysmex UF-5000 with manual Gram stain and urine culture results

Dietmar Enko, Ingeborg Stelzer, Michael Böckl, Wolfgang J. Schnedl, Andreas Meinitzer, Markus Herrmann, Martin Tötsch and Michael Gehrer

Abstract

Objectives

Recently, the fully automated flow cytometry-based UF-5000 (Sysmex Corboration, Kobe, Japan) urine sediment analyzer was developed providing bacteria (BACT) info flags for more accurate bacterial discrimination of urinary tract infections (UTIs). This study aimed to compare the reliability of the UF-5000 BACT-info flags with manual Gram stain and urine culture as the gold standard method.

Methods

A total of 344 urine samples were analyzed on the UF-5000 and compared with manual microscopic Gram stain and urine cultures. Agreement was assessed by Cohen’s kappa (κ) analysis. The Youden index was used to determine the optimal BACT and white blood cell (WBC) cut-off points for discriminating positive and negative urine cultures.

Results

Overall 98/344 (28.5%) samples were urine culture positive at a cut-off of ≥105 CFU/mL. “Gram-negative?” UF-5000 BACT-Info flags showed a better concordance of 25/40 (62.5%) with urine culture compared to Gram stain with 30/50 (60%). The results for UF-5000 discrimination of Gram-positive and Gram-negative microorganisms demonstrated a substantial (κ = 0.78) and fair (κ = 0.40) agreement with urine culture. Optimal cut-off points detecting positive urine cultures were 135 BACT/µL (sensitivity [SE]: 92.1%, specificity [SP]: 85.4%, positive predictive value [PPV]: 71%, negative predictive value [NPV]: 96%) and 23 WBC/µL (SE: 73.5%, SP: 84.1%, PPV: 65%, NPV: 89%).

Conclusions

The UF-5000 analyzer (Sysmex) is a reliable diagnostic tool for UTI screening. The displayed BACT-Info flags allow a quick diagnostic orientation for the clinician. However, the authors suggest verifying the automated Gram categories with urine culture.


Corresponding author: Dietmar Enko, MD, Clinical Institute of Medical and Chemical Laboratory Diagnostics, Medical University of Graz, Auenbruggerplatz 15, 8036 Graz, Austria; Institute of Clinical Chemistry and Laboratory Medicine, General Hospital Hochsteiermark, Leoben, Austria, Phone: +43 316 385-13145, Fax: +43 316 385-13430, E-mail:

  1. Research funding: None declared.

  2. Author contributions: DE wrote the manuscript and supervised this study project. All authors have accepted responsibility for the entire content of this manuscript and approved its submission.

  3. Competing interests: Authors state no conflict of interest.

  4. Informed consent: Informed consent was not required because the urine samples were submitted for routine analysis only and patient data were anonymous.

  5. Ethical approval: The ethical approval of this study was provided by the Ethical Committee of the Medical University Graz (Graz, Austria) and carried out with the current version of the Declaration of Helsinki.

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Received: 2020-08-19
Accepted: 2020-09-27
Published Online: 2020-10-12
Published in Print: 2021-02-23

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