Urine flow cytometry as a primary screening method to exclude urinary tract infections
Clinical Laboratory, Catharina Hospital Eindhoven, Michelangelolaan 2, 5623 EJ, Eindhoven, The Netherlands, . World Journal of Urology
(Impact Factor: 2.67).
05/2012; 31(3). DOI: 10.1007/s00345-012-0883-4
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.
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.
18 % of cultures were positive, defined as >104 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 %).
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.
Available from: Stanley Cheung
- "However, these tests have a limited diagnostic accuracy. Typically, a high sensitivity is achieved at the expense of specificity or vice versa  . Moreover, the subjective visual assessment of the strip can introduce an error rate up to 12%, and instrument-based reading still results in an error rate of approximately 3% . "
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Urinary tract infection (UTI) is one of the most common bacterial infections in humans; however, there is no accurate and fast quantitative test to detect UTI. Dipstick urinalysis is semi-quantitative with a limited diagnostic accuracy, while urine culture is accurate but takes time. We described a quantitative biochemical method for the diagnosis of bacteriuria using a single marker.
We compared the urine metabolomes from 88 patients with bacterial UTI and 61 controls using (1)H NMR spectroscopy followed by principal component analysis (PCA) and orthogonal partial least squares-discriminant analysis (OPLS-DA). The biomarker identified was subsequently validated using independent samples.
The urine acetic acid/creatinine (mmol/mmol) level was determined to be the most discriminatory marker for bacterial UTI with an area-under-receiver operating characteristic curve=0.97, sensitivity=91% and specificity=95% at the optimal cutoff 0.03 mmol/mmol. For validation, 60 samples were recruited prospectively. Using the optimal cutoff for acetic acid/creatinine, this method showed sensitivity=96%, specificity=94%, positive predictive value=92%, negative predictive value=97% and an overall accuracy=95%. The diagnostic performance was superior to dipstick urinalysis or microscopy. In addition, we also observed an increase of urinary trimethylamine (TMA) in patients with Escherichia coli-associated UTI. TMA is a mammalian-microbial co-metabolite and the high level of TMA generated is related to the bacterial enzyme, trimethylamine N-oxide (TMAO) reductase which reduces TMAO to TMA.
Urine acetic acid is a neglected metabolite that can be used for rapid diagnosis of UTI and TMA can be used for etiologic diagnosis of UTI. With the introduction of NMR-based clinical analyzers to clinical laboratories, NMR-based urinalysis can be translated for clinical use.
Available from: Abu-Bakr M. Gomaa
- "The percent of asymptomatic individual (have infection without symptoms) was 3.7%, from those asymptomatic individuals 33% infected by E. coli, 33% by Pseudomonas, 22% by Klebsiella and 11% by Citrobacter (Table 3). By suing the 4 flow cytometry method, each bacterium was measured; low detection limit was 6.0×10 cell/ml and quantification limits was 3 5.1×10 cell/ml; the obtained results were found in agreement with Fabbro et al. (2011) and Boonen et al. (2012). 5 5 All published studies on this issue have used an older microbiological threshold of ¡Ý 10 CFU/ml. "
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ABSTRACT: The aim of this study is to determine the cutoff numbers of bacteria and percentages of the asymptomatic human urinary tract infections UTI - causing E. coli in Saudi Arabia. Because (UTIs) are a quite common disease. The urine culture is the gold standard to count the bacteria and diagnosing UTIs, but most clinical samples yield negative results and it is time consuming. The automated methods are high sensitive to all types of bacteria vegetated, non-vegetated and/or dead bacteria. Both a fully automated methods have been used by using fluorescent flow cytometery particle analyzer (UF-1000i) and VITEK® 2 for bacteria identification, then the conventional methods of microscopic examination, urine culture and API for bacteria identification were integrated. The results for flow cytometry method 4 indicate that the upper limit (cutoff) for bacteria in males in Saudi Arabia is up to 7.8x10/ml for male, and 4 up to 8.8x10/ml in females. The Microscopic method results indicate that the upper limit for bacteria in 44 males in Saudi Arabia is 6x10/ml, and up to 7.0x10/ml, in females, which are less than the traditional 5 cutoff (bacteria count >10 bacteria/ml). The percentage of asymptomatic individuals (have infection without symptoms) was 3.7%, from those infected individuals: 33% infected by E. coli, 33% by Pseudomonas, 22% by Klebsiella and 11% by Citrobacter.
Available from: Yasemin Budak
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ABSTRACT: Urinary tract infection (UTI) is one of the most common types of infection. Currently, diagnosis is primarily based on microbiologic culture, which is time- and labor-consuming. The aim of this study was to assess the diagnostic accuracy of urinalysis results from UriSed (77 Electronica, Budapest, Hungary), an automated microscopic image-based sediment analyzer, in predicting positive urine cultures.
We examined a total of 384 urine specimens from hospitalized patients and outpatients attending our hospital on the same day for urinalysis, dipstick tests and semi-quantitative urine culture. The urinalysis results were compared with those of conventional semiquantitative urine culture.
Of 384 urinary specimens, 68 were positive for bacteriuria by culture, and were thus considered true positives. Comparison of these results with those obtained from the UriSed analyzer indicated that the analyzer had a specificity of 91.1%, a sensitivity of 47.0%, a positive predictive value (PPV) of 53.3% (95% confidence interval (CI) = 40.8-65.3), and a negative predictive value (NPV) of 88.8% (95% CI = 85.0-91.8%). The accuracy was 83.3% when the urine leukocyte parameter was used, 76.8% when bacteriuria analysis of urinary sediment was used, and 85.1% when the bacteriuria and leukocyturia parameters were combined. The presence of nitrite was the best indicator of culture positivity (99.3% specificity) but had a negative likelihood ratio of 0.7, indicating that it was not a reliable clinical test.
Although the specificity of the UriSed analyzer was within acceptable limits, the sensitivity value was low. Thus, UriSed urinalysis resuIts do not accurately predict the outcome of culture.
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