Regístrese
Buscar en
Enfermedades Infecciosas y Microbiología Clínica
Toda la web
Inicio Enfermedades Infecciosas y Microbiología Clínica Evaluation and optimization of the Sysmex UF1000i system for the screening of ur...
Información de la revista
Vol. 33. Núm. 5.
Páginas 320-323 (Mayo 2015)
Compartir
Compartir
Descargar PDF
Más opciones de artículo
Visitas
2700
Vol. 33. Núm. 5.
Páginas 320-323 (Mayo 2015)
Original
DOI: 10.1016/j.eimc.2014.07.010
Acceso a texto completo
Evaluation and optimization of the Sysmex UF1000i system for the screening of urinary tract infection in primary health care elderly patients
Evaluación y optimización del sistema Sysmex UF-1000i como método de cribaje para el estudio de infecciones urinarias en pacientes ancianos de Atención Primaria
Visitas
2700
Guillermo Martín-Gutiérreza,
Autor para correspondencia
guiller_mg86@hotmail.es

Corresponding author.
, Ana Porras-Gonzáleza, Carlos Martín-Pérezb, Jose Antonio Lepea,c, Javier Aznara,c
a Infectious Diseases, Clinical Microbiology and Preventive Medicine Unit, Hospital Universitario Virgen del Rocío, Seville, Spain
b UGC Marquesado, AGS Nordeste de Granada; SAMSERAP group, Spain
c Institute of Biomedicine of Seville (IBiS), University Hospital Virgen del Rocío/CSIC/University of Seville, Seville, Spain
Este artículo ha recibido
2700
Visitas
Información del artículo
Resumen
Texto completo
Bibliografía
Descargar PDF
Estadísticas
Figuras (1)
Tablas (2)
Table 1. Parameters depending on the cut-off values for the bacterial count.
Table 2. Number and percentage of savings with different cut-off values.
Mostrar másMostrar menos
Abstract
Objective

Urinary tract infections (UTIs) are a common problem in the elderly population. Urine culture is still considered the “gold standard” to diagnose infection in this population. However, urine cultures are laborious and costly, and most samples will yield no growth.

Methods

An evaluation was made of the Sysmex UF-1000i flow cytometer as a screening tool for UTI in an elderly population older than 65 years who lived in the community, using 346 urine samples submitted for culture.

Results

The Receiver Operating Characteristic (ROC) analysis showed a significant difference (P<0.01) between 0.98 bacteria area under the curve value and 0.82 of white blood cells (WBC). The combination of both counts for screening did not show any improvement in specificity or sensitivity. According to our data, the use of a single cut-off point of 200bacteria/μL is suggested, in which the sensitivity and specificity were 99.11% and 91.59%, respectively, with a NPV of 99.49%. Moreover, this cut-off value could avoid 60.24% of the samples to be cultured, with a minimal false negative results rate of 0.87%.

Conclusions

The stratification of age groups stratification helps in selecting a more adjusted Sysmex UF1000i cut-off limit, leading to an improvement in the screening parameters that would imply a better management of these infections, as well as a high reduction in the workload and cost savings.

Keywords:
UTI
Elderly
Flow cytometry
Resumen
Objetivo

Evaluar y optimizar el uso del citómetro de flujo (Sysmex UF1000i®) como cribado para las infecciones urinarias (ITUs) en pacientes ≥65 años procedentes de Atención Primaria.

Métodos

Se estudiaron 346 orinas de pacientes ≥65 años con sospecha de infección urinaria, enviadas al Hospital Universitario Virgen del Rocío, durante el periodo enero-mayo 2013. Las muestras se estudiaron mediante citometría de flujo y cultivo cuantitativo en medio cromogénico.

Resultados

Se incluyeron 346 pacientes, cuya edad media fue de 76,70±0,75 años. De las 346 muestras 113 (32,65%) fueron positivas, 214 (61,84%) negativas y 19 (5,49%) contaminadas. El área bajo la curva ROC utilizando el número de bacterias (0,98) fue mayor que para los leucocitos (0,82), existiendo diferencias significativas entre ellas (P<0.01). El estudio conjunto de bacterias y leucocitos no supuso ninguna mejora, por lo que se utilizaron distintos umbrales basados en el número de bacterias. De acuerdo con nuestros datos, proponemos un punto de corte de 200 bacterias/μl con el cual obtenemos una sensibilidad del 99,11% y especificidad del 91,59%, con un valour predictivo negativo del 99,49%. Además este punto de corte nos permitiría evitar el 60,24% de los cultivos, con una mínima tasa de falsos negativos (0,87%).

Conclusiones

La categorización de la población según criterios de positividad para el diagnóstico de la ITU, así como en grupos etarios con las mismas condiciones clínicas, permite incrementar la exactitud de los resultados obtenidos, reduciendo la carga de trabajo sustancialmente así como los costes asociados.

Palabras clave:
UTI
Mayores
Citómetro de flujo
Texto completo
Introduction

In the elderly population urinary tract infections (UTIs) are common, representing the second most frequent infection in elderly women living in the community.1,2 The diagnosis of UTI requires the presence of significant bacteriuria (≥105 Colony Forming Unit (CFU) per mL) and genitourinary symptoms. However, these patients may not refer typical urinary complaints; thus, the diagnosis may be more challenging than in other age groups. Most of these cases are self-limited and have no long-term sequelae, but underlying structural or functional abnormalities of the genitourinary tract are not rare,3 and serious complications may develop, such as pyelonephritis or sepsis.4,5

Microbiologic cultures are still considered the diagnostic “gold standard”, allowing identification and quantification of the causal agents.6 Nevertheless, culturing of the samples is both time and labour consuming, with most of the samples yielding no growth.3,7,8 Screening methods can improve the laboratory efficiency by ruling out UTI-negative samples, thereby reducing the workload. The Sysmex UF-1000i (TOA Medical Electronics, Kobe, Japan) is an automated urine particle analyzer using laser-based fluorescent flow cytometry. Some data have shown that it is valid as a screening test for UTIs, suggesting that cut-off values should vary depending on both age and gender.9–11 Further studies are required to establish the value of this system, interpret the results and adapt the criteria of a positive result to the characteristics of a given population.

In 2012, 34,128 urine samples from Primary Care Units were received at the Microbiology Service of the Virgen del Rocío University Hospital, out of which 10,223 (29.95%) were from elderly patients, 70% being negative cultures (data not shown). This high number of negative specimens emphasizes the need for a urine samples screening method prior to be cultured, and therefore to improve the laboratory efficiency by reducing not only the economical and workload costs but also by shortening the laboratory response time.

The aim of this study was to evaluate and to optimize the use of the Sysmex UF-1000i as a screening method for urine samples obtained from an in community-dwelling elderly population older than 65 year.

Materials and methodsPatients and urine samples

From January 2013 to June 2013, 346 patients attending at the Primary Care Units of Virgen del Rocío University Hospital were selected using a systematic random sampling. Four to five urine samples per day submitted for culture from elderly outpatients (≥65 years old) were randomly selected. Sample size was determined by the Carley et al. method,12 using a 95% of sensitivity and a precision of 5% for the expected UTI prevalence of elderly patients. Midstream catch urine was collected in sterile preservative tubes SRO-1-25B with boric acid (Soria Melguizo S.A., Madrid, Spain), transported at cold temperature and processed within 4–8h after the sampling.

Culture and urinalysis

Ten microlitres of the urine specimen were quantitatively cultured onto Brilliance UTI Clarity Agar (Oxoid, Basingstoke, UK) plates. All plates were aerobically incubated for 18–24h at 37°C, and the results were expressed as the number of colony-forming units (CFUs) per millilitre. A threshold of ≥105CFUs/mL for women and ≥104CFUs/mL for men was established for positive cultures. The presence of two or more different isolates as well as the growth of one or more non-pathogens was defined as contamination of the specimen. Identification of the isolates was performed by conventional biochemical tests (biochemical testing, pigment production, growth, and colony characteristics) and MicroScan WalkAway®plus System (Siemens Healthcare Diagnostics, WestSacramento, CA). When the identification was uncertain, it was confirmed by Bruker Biotyper MALDI-TOF MS system (Bruker Daltonik GmbH, Leipzig, Germany).

All of the urine specimens were also analyzed by the Sysmex UF-1000i, which allows the discrimination and quantification of bacteria, erythrocytes, WBC, epithelial cells, casts, crystals, fungi, and sperm. The results obtained with Sysmex UF-1000i and those from the urine cultures were compared.

Statistics

A logistic regression model was performed, in which age, gender, bacterial count and WBC count were included as independent variables, to predict the probability of a positive culture. The cut-off values for bacteria and leucocytes were evaluated in the Sysmex UF-1000i according to the area under the ROC curve, which was estimated by using the Hanley and McNeil's nonparametric method.13 The bacteria and leucocytes ROC curves were compared by the De Long et al. method.14 Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were calculated for those cut-off points. A P value ≤0.05 was considered as significant. The data analysis was carried out using the software STATA Release 10.1 statistical package (StataCorp LP, Lakeway Drive, TX, USA).

Results

In total, 346 elderly patients, 261 women (75, 43%) and 85 men (24, 56%) were included in this study. The mean age was 76.70±0.75 years. One hundred and thirteen (32.65%) of the urine samples yielded positive cultures, 214 (61.84%) were negative and 19 (5.49%) were considered as contaminated and not further tested. The clinical isolates obtained were: Escherichia coli (72), Klebsiella pneumoniae,13Proteus mirabilis,9Enterococcus faecalis,5Pseudomonas aeruginosa,4 ESBL-E. coli,3 ESBL-K. pneumoniae,1Klebsiella oxytoca,1Serratia liquefaciens,1Morganella morgani,1Citrobacter freundii,1Citrobacter koseri1 and Citrobacter amalonaticus.1

The ROC curves for WBC and bacterial counts from the UF-1000i are given in Fig. 1. The area under the curve (AUC) for bacterial counts was 0.98, a significantly higher value than the 0.82 AUC for WBC count (P<0.01). WBC count was not as effective as the former as screening method for UTI, and the use of both bacterial and WBC counts did not show any advantage in terms of sensitivity or specificity compared with bacterial counts alone. Therefore, only different cut-off values for bacterial counts have been applied to predict community-acquired UTI in the elderly. Parameters associated with the different cut-off values for bacterial counts generated by Sysmex UF-1000i are shown in Table 1.

Fig. 1.

Receiver operating characteristic curve of bacterial and WBC counts on the UF-1000i flow cytometer.

(0,14MB).
Table 1.

Parameters depending on the cut-off values for the bacterial count.

Definition  Sa  95% CI  SPa  95% CI  PPVa  95% CI  NPVa  95% CI 
≥ 50bacteria/μL  100  96.71–100  73.83  67.55–79.26  66.86  59.46–73.51  100  97.62–100 
≥100bacteria/μL  100  96.71–100  83.18  77.59–87.59  75.84  68.37–82.00  100  97.89–100 
≥150bacteria/μL  99.11  95.16–99.84  87.38  82.26–91.18  80.57  73.21–86.29  99.47  97.05–99.91 
≥200bacteria/μL  99.11  95.16–99.84  91.59  87.09–94.61  86.15  79.17–91.06  99.49  97.18–99.91 
≥250bacteria/μL  96.46  91.25–98.61  92.06  87.64–94.98  86.50  79.45–91.40  98.00  94.99–99.22 
≥300bacteria/μL  93.80  87.76–96.97  92.52  88.20–95.34  86.88  79.75–91.76  96.58  93.12–98.33 
≥350bacteria/μL  92.92  86.65–96.37  94.39  90.45–96.76  89.74  82.92–94.03  96.19  92.66–98.05 
a

S, sensitivity; SP, specificity; PPV, positive predictive value; NPV, negative predictive value.

The most balanced cut-off value was 338bacteria/μL, with sensitivity, specificity and negative predictive (NP) values of 93.81%, 93.93% and 96.39% respectively. Nevertheless, screening for negative urine samples requires both a high sensitivity and high NP values in order to minimize the number of false-negative results. Sensitivity and specificity values of 99.11% and 91.59% respectively, with a NPV of 99.49% (Table 2) were obtained with a cut-off of 200bacteria/μL.

Table 2.

Number and percentage of savings with different cut-off values.

Definition  No. necessary cultures  No. unnecessary cultures  % unnecessary cultures  % false negatives  95% CI 
≥50bacteria/μL  169  158  48.32  0–3.29 
≥100bacteria/μL  149  178  54.43  0–3.29 
≥150bacteria/μL  139  188  57.49  0.87  0.17–4.84 
≥200bacteria/μL  130  197  60.24  0.87  0.17–4.84 
≥250bacteria/μL  126  201  61.47  3.54  1.38–8.75 
≥300bacteria/μL  121  206  63.00  6.19  3.03–12.28 
≥350bacteria/μL  117  210  64.22  7.08  3.63–13.35 
Discussion

Several studies, with a considerable heterogeneity in variables such as gender, age or clinical condition (in or outpatients, comorbidities, use of medical devices, etc) have shown the usefulness of the UF-1000i screening for UTI.4,6,9 The use of a unique standard cut-off value for a heterogeneous population results in over- or under-culturing specimens among different groups, thereby affecting both predictive values and diminishing the reliability of the screening. In addition, stratification according to different established UFC/mL criteria for the diagnosis of UTI is likely to increase the accuracy of the studies’ results in different groups of populations.15 These and other factors should be also considered when deciding the proper cut-off value in a precise group of population. Regarding elderly people, the criteria of 105UFC/mL for women and 104UFC/mL for men meet the standard one, but the higher prevalence of UTI increases the PPV and decreases the NPV. Moreover, misclassification of patients with or without UTI may have serious implications due to frequent presence of multimorbidity, polytreatment and impaired renal function in this age group. All these factors emphasize the convenience to lower the ROC curve most balanced cut-off value in order to raise both sensitivity and NPV, and therefore to achieve a lower false negative rate. In addition, fast and reliable negative results may allow an antibiotic treatment discontinuation, bringing along a decrease in the risk of drug interactions and side effects in an often-multimorbid patient.

In our study, the sensitivity, specificity, and AUC of bacterial count in the Sysmex UF-1000i analyzer system were higher than those of WBC count, and the combination of both counts for screening did not show any specificity or sensitivity improvements to bacterial counts alone, as previously reported.7 Nevertheless, in contrast with these results, some articles showed the effectiveness of screening with WBC plus bacterial counts,6,10 with an increase in sensitivity but a decrease in specificity. This difference could be attributable to the two different populations studied, outpatients only7 or both in- and outpatients.6,10 Moreover, some studies reveal that pyuria is not a good marker of UTI. In the study by Kishore et al., the relationship between pyuria and culture positivity did not reach statistical significance in both males and females in the community elderly.16 Another study performed by Kupelian et al.17 reported that pyuria demonstrates poor sensitivity in patients with UTI. A systematic review and meta-analysis performed by Shang et al. conclude that UF-1000i may be used as an effective screening method for UTI by measuring WBC and bacterial counts of urine samples.18 Nevertheless, in this study the overall estimates of sensitivity and specificity show a very high heterogeneity (i2>90%), limiting the validity of these results. Broeren et al.3 hypothesized that the lack of improvement shown in some studies was due to the lack of use of boric acid, which acts as a stabilizing compound. Kupelian et al.17 describes that cell destruction appears to be retarded by boric acid, although significant cell loss appears inevitable. Our data do not support this hypothesis, as we used boric acid containers and no improvement was observed. It has been suggested that gender-specific cut-off points could improve the screening,10 but again we did not find any significant differences between men and women for bacterial counts.

According to our data, the recommended cut-off value is 200bacteria/μL, higher than those mentioned in previous studies,6,7,19–22 and with which, we obtain a 60, 24% reduction of the samples to be cultured, with a very low 0.87% false negative rate. The only false negative culture result found was a>105CFU/mL Proteus mirabilis culture. False negative results mainly with Gram-positive pathogens,14,17 but also with Gram-negatives have been documented with the use of Sysmex UF-1000i.23,24 Further studies using larger sample sizes would probably permit to address this issue. A limitation in the design of our study is that the cohort was selected from urine samples sent to the laboratory instead of from a group of patients eligible for UTI.

Conclusions

In conclusion, age-groups stratification allows selecting a more adjusted Sysmex UF1000i cut-off, bringing along an improvement in the screening parameters that would imply a high reduction in the workload and cost savings. In the community-dwelling elderly and according to our data, a 200bacteria/μL cut-off value should be used. This would mean reducing waiting times in the case of negative cultures, thus eliminating possible antibiotic adverse effects and interactions, with a minimal false negatives rate. Further prospective studies are needed in order to contrast these data with larger populations, and to establish the more convenient cut-off for each group of patients.

Conflict of interest

The authors declare no conflict of interest.

References
[1]
S.J. Matthews, J. Lancaster.
Urinary tract infections in the elderly population.
Am J of Geriatr Pharmacother, 9 (2011), pp. 286-309
[2]
G. Schmiemann, E. Kniehl, K. Gebhardt, M.M. Matejczyk, E. Hummers-Pradier.
The diagnosis of urinary tract infection. A systematic review.
Dtsch Arztebl Int, 107 (2010), pp. 361-367
[3]
L.A. Beveridge, P.G. Davey, G. Phillips, M.E. McMurdo.
Optimal management of urinary tract infections in older people.
Clin Interv Aging, 6 (2011), pp. 173-180
[4]
M.A. Broeren, S. Bahceci, H.L. Vader, N.L. Arents.
Screening for urinary tract infection with the Sysmex UF-1000i urine flow cytometer.
J Clin Microbiol, 49 (2011), pp. 1025-1029
[5]
M. Yates.
Urinary tract infection in the elderly.
Aust J Hosp Pharmacy, 29 (1999), pp. 166-170
[6]
J. Gutiérrez-Fernández, A. Lara, M.F. Bautista, J. de Dios Luna, P. Polo, C. Miranda, et al.
Performance of the Sysmex UF1000i system in screening for significant bacteriuria before quantitative culture of aerobic/facultative fast-growth bacteria in a reference hospital.
J Appl Microbiol, 113 (2012), pp. 609-614
[7]
X. Hu, J. Zhang, X. Zhang.
Evaluation of the Sysmex UF-1000i urine analyzer as a screening test to reduce the need for urine cultures for urinary tract infection.
Lab Med, 41 (2010), pp. 349-352
[8]
S.Y. Kim, Y.J. Kim, S.M. Lee, S.H. Hwang, H.H. Kim, H.C. Son, et al.
Evaluation of the Sysmex UF-100 urine cell analyzer as a screening test to reduce the need for urine cultures for community-acquired urinary tract infection.
Am J Clin Pathol, 128 (2007), pp. 922-925
[9]
B. Pieretti, P. Brunati, B. Pini, C. Colzani, P. Congedo, M. Rocchi, et al.
Diagnosis of bacteriuria and leukocyturia by automated flow cytometry compared with urine culture.
J Clin Microbiol, 48 (2010), pp. 3990-3996
[10]
C.D. Giesen, A.M. Greeno, K.A. Thompson, R. Patel, S.M. Jenkins, J.C. Lieske.
Performance of flow cytometry to screen urine for bacteria and white blood cells prior to urine culture.
Clin Biochem, 46 (2013), pp. 810-813
[11]
S. Jolkkonen, E.L. Paattiniemi, P. Kärpänoja, H. Sarkkinen.
Screening of urine samples by flow cytometry reduces the need for culture.
J Clin Microbiol, (2010), pp. 3117-3122
[12]
S. Carley, S. Dosman, S.R. Jones, M. Harrison.
Simple nomograms to calculate sample size in diagnostic studies.
Emerg Med J, 22 (2005), pp. 180-181
[13]
J.A. Hanley, B.J. McNeil.
The meaning and use of the area under a receiver operating characteristic (ROC) curve.
[14]
E.R. De Long, D.M. De Long, D.L. Clarke-Pearson.
Comparing the areas under two or more correlated receiver operating characteristic curves: a nonparametric approach.
Biometrics, 44 (1988), pp. 837-845
[15]
M.J. Kubik, Y.S. McCarter.
Controversies in the diagnosis of urinary tract infections.
Clin Microbiol Newslett, 34 (2012), pp. 185-191
[16]
D. Kishore, I.S. Gambhir, A. Diwaker, V. Khurana, R. Dant, S. Anupurba.
Study of urinary infection in community based indian elderly.
Indian J Res, 7 (2013), pp. 32-39
[17]
A.S. Kupelian, H. Horsley, R. Khasriya, R.T. Amussah, R. Badiani, A.M. Courtney, et al.
Discrediting microscopic pyuria and leucocyte esterase as diagnostic surrogates for infection in patients with lower urinary tract symptoms: results from a clinical and laboratory evaluation.
[18]
Y. Shang, Q. Wang, J. Zhang, Y. Xu, W. Zhang, Y. Chen, et al.
Systematic review and meta-analysis of flow cytometry in urinary tract infection screening.
Clin Chim Acta, 424 (2013), pp. 90-95
[19]
J. Krongvorakul, S. Phundhusuwannakul, P. Santanirand, M. Kunakorn.
A flow cytometric urine analyzer for bacteria and white blood cell counts plus urine dipstick test for rapid screening of bacterial urinary tract infection.
Asian Biomed, 6 (2012), pp. 601-608
[20]
M. Muñoz-Algarra, R. Martínez-Ruiz, B. Orden-Martínez.
Evaluación del sistema automatizado UF-1000i®en el diagnóstico de infección urinaria.
Enferm Infecc Microbiol Clin, 31 (2013), pp. 29-31
[21]
J. Wang, Y. Zhang, D. Xu, W. Shao, Y. Lu.
Evaluation of the Sysmex UF-1000i for the diagnosis of urinary tract infection.
Am J Clin Pathol, 133 (2010), pp. 577-582
[22]
K. Kadkhoda, K. Manickam, P. Degagne, P. Sokolowski, P. Pang, N. Kontzie, et al.
UF-1000i flow cytometry is an effective screening method for urine specimens.
Diagn Microbiol Infect Dis, 69 (2011), pp. 130-136
[23]
R. De Rosa, S. Grosso, G. Bruchetta, M. Avolio, P. Stano, M.L. Modolo.
Evaluation of the Sysmex UF 1000i flow cytometer for ruling out bacterial urinary tract infection.
Clin Chim Acta, 411 (2010), pp. 1137-1142
[24]
F. Manoni, L. Fornasiero, M. Ercolin, A. Tinello, M. Ferrian, P. Hoffer, et al.
Cutoff values for bacteria and leukocytes for urine flow cytometer Sysmex UF-1000i in urinary tract infections.
Diagn Microbiol Infect Dis, 65 (2009), pp. 103-107
Copyright © 2014. Elsevier España, S.L.U. y Sociedad Española de Enfermedades Infecciosas y Microbiología Clínica
Opciones de artículo
Herramientas
es en pt

¿Es usted profesional sanitario apto para prescribir o dispensar medicamentos?

Are you a health professional able to prescribe or dispense drugs?

Você é um profissional de saúde habilitado a prescrever ou dispensar medicamentos

es en pt
Política de cookies Cookies policy Política de cookies
Utilizamos cookies propias y de terceros para mejorar nuestros servicios y mostrarle publicidad relacionada con sus preferencias mediante el análisis de sus hábitos de navegación. Si continua navegando, consideramos que acepta su uso. Puede cambiar la configuración u obtener más información aquí. To improve our services and products, we use "cookies" (own or third parties authorized) to show advertising related to client preferences through the analyses of navigation customer behavior. Continuing navigation will be considered as acceptance of this use. You can change the settings or obtain more information by clicking here. Utilizamos cookies próprios e de terceiros para melhorar nossos serviços e mostrar publicidade relacionada às suas preferências, analisando seus hábitos de navegação. Se continuar a navegar, consideramos que aceita o seu uso. Você pode alterar a configuração ou obter mais informações aqui.