Evaluation of three bacteriuria screening methods in a clinical research hospital

Analysis of the costs for the laboratory of flow cytometry screening of urine samples before culture

Urine culture samples comprise a large proportion of the workload in clinical microbiology laboratories, and most of the urine samples show no growth or insignificant growth. A flow cytometry-based analyzer (Sysmex Corporation, Japan) has been used to screen out negative urine samples prior to culture in the Päijät-Häme district. We applied decision analytic modelling to analyze, from a laboratory perspective, the economic feasibility of the screening method as compared to culture only (conventional method) for diagnosis of urinary tract infection. Our model suggests that the least costly analytical strategy is the conventional method. The incremental cost of screening is €0.29/sample. Although laboratory costs are higher, considerable savings on workload can be achieved. Furthermore, screening has numerous benefits on the treatment process of a patient that well warrant the use of the screening method. We conclude that the incremental cost of screening the samples is worth the expense.

Evaluation of an Image Analysis Device (APAS) for Screening Urine Cultures

While advancements have been made in some areas of pathology with diagnostic materials being screened using image analysis technologies, the reporting of cultures from agar plates remains a manual process. We compared the results for 2,163 urine cultures read by a reference panel of microbiologists, by the routine laboratory process, and by an automated plate reading system, APAS (LBT Innovations Ltd., South Australia). APAS detected colonies with a sensitivity of 99.1% and a specificity of 99.3% on blood agar, while on MacConkey agar, the colony detection sensitivity was 99.4% with a specificity of 99.3%. The device's ability to enumerate growth had an accuracy of 89.2%, and the morphological identification of colonies showed a high level of performance for the colony types typical of Escherichia coli and other enteric bacilli. On blood agar, lactose-fermenting colonies were morphologically identified with a sensitivity of 98.9%, while on MacConkey agar they were identified with a sensitivity of 99.2%. In this first clinical evaluation, APAS demonstrated high performance in the detection, enumeration, and colony classification of isolates compared with that for conventional plate-reading methods. The device found all cases reported by the laboratory and detected the most commonly encountered organisms found in urinary tract infections.

Does flow cytometry have a role in preliminary differentiation between urinary tract infections sustained by gram positive and gram negative bacteria? An Italian polycentric study

BACKGROUND

Urine culture is the most frequently requested test for a Microbiology Lab. A reliable screening tool would be of paramount importance both to clinicians and laboratorians, provided that it could get fast and accurate negative results in order to rule-out urinary tract infection (UTI).

MATERIALS AND METHODS

We evaluated 1907 consecutive urine samples from outpatients. Culture was performed on chromogenic agar with 1μL loop, using 10(5)CFU/mL as a limit of positive growth. Using Sysmex Uf-1000i analyzer we evaluated bacteria forward scatter (B_FSC) and fluorescent light scatter (B_FLH) in a preliminary discrimination step for UTI caused by Gram+ or Gram- bacteria.

RESULTS

We got 512 positive samples. A mono-microbial infection was observed in 490 samples; two bacterial strains were isolated in 22 samples, so 534 bacterial strains were found: 392 Gram-, 133 Gram+ and 9 yeasts. Comparing Gram+ and Gram- bacteria we observed a statistically significant difference for B_FSC but not for B_FLH. In this application experimental cut-off value for B_FSC was 25ch. Using this cut-off to perform a presumptive identification of UTI sustained by Gram-+ bacteria, we observed a SE 0.68, SP 0.84.

CONCLUSION

Our data although preliminary suggest that B_FSC could be useful in presumptive exclusion of UTI caused by Gram-positive bacteria.

Screening of urine samples by flow cytometry reduces the need for culture

Urine samples constitute a large proportion of samples tested in clinical microbiology laboratories. Culturing of the samples is fairly time- and labor-consuming, and most of the samples will yield no growth or insignificant growth. We analyzed the feasibility of the flow cytometry-based UF-500i instrument (Sysmex, Japan) to screen out urine samples with no growth or insignificant growth and reduce the number of samples to be cultured. A total of 1,094 urine specimens sent to our laboratory for culture during 4 months in the spring of 2009 in Lahti, Finland, were included in the study. After culture, all samples were analyzed with the Sysmex UF-500i for bacterial and leukocyte (white blood cell [WBC]) counts. Youden index and closest (0,1) methods were used to determine the cutoff values for bacterial and WBC counts in culture-positive and -negative groups. By flow cytometry, samples considered positive for UTI in culture had bacterial and WBC values that were significantly higher than those for samples considered negative. The flow cytometric screening worked best when both bacterial counts and WBC counts were used with age- and gender-specific cutoff values for all patient groups, excluding patients with urological disease or anomaly. By use of these cutoff values, 5/167 (3.0%) of culture-positive samples were missed by UF-500i and the percentage of samples that did not need to be cultured was 64.5%. Use of the UF-500i instrument is a reliable method for screening out a major part of the UTI-negative samples, significantly diminishing the amount of work required in the microbiology laboratory.

Unsatisfactory performance of flow cytometer UF-100 and urine strips in predicting outcome of urine cultures

UF-100 flow cytometer and urine strip results were cross-interpreted to predict culture outcomes. The best negative predictive value was obtained with bacteria at > or =1,000/microl, white blood cells at > or =20/microl, or leukocyte esterase positivity. Nine of 24 false negatives were clinically significant. Thus, UF-100 and urine strip results do not accurately predict the outcome of cultures.

Simplified technique for detection of significant bacteriuria by microscopic examination of urine

A comparative study of microscopic examination of 10 microl (simplified loop technique) and 50 microl (traditional drop technique) of uncentrifuged Gram-stained urine specimens for detection of significant bacteriuria was carried out. The results demonstrated that the 10-microl loop technique can be used as an alternative to the 50-microl drop technique for presumptive diagnosis of urinary-tract infection in bacteriological practice, with the advantages of greater rapidity and ease of performance.

Rapid bioluminescence method for bacteriuria screening

A study was performed to evaluate the UTIscreen (Los Alamos Diagnostics, Los Alamos, N. Mex.), a rapid bioluminescence bacteriuria screen. The UTIscreen was compared with three other rapid bacteriuria screens: the Bac-T-Screen (Vitek Systems, Hazelwood, Mo.), an automated filtration device; the Chemstrip LN (Boehringer Mannheim Diagnostics, BioDynamics, Indianapolis, Ind.), an enzyme dipstick; and the Gram stain. A semiquantitative plate culture was used as the reference method. Of the 1,000 specimens tested, 276 had colony counts of greater than 10(5) CFU/ml by the culture method. Of these, the UTIscreen detected 96% (265 of 276) using greater than or equal to 5% of the integrated light output of the standard reading as a positive interpretive breakpoint, the Bac-T-Screen detected 96% (266 of 276), the Chemstrip LN detected 90% (249 of 276), and the Gram stain detected 96% (264 of 276). Of the 214 probable pathogens isolated at greater than 10(5) CFU/ml, the UTIscreen detected 95% (204 of 214), the Bac-T-Screen detected 98% (210 of 214), the Chemstrip LN detected 92% (198 of 214), and the Gram stain detected 98% (209 of 214). The predictive values of negative test results at greater than 10(5) CFU/ml for the UTIscreen, the Bac-T-Screen, the Chemstrip LN, and the Gram stain were 98, 97, 93, and 98%, respectively. The overall specificities at greater than 10(5) CFU/ml for the UTIscreen, the Bac-T-Screen, the Chemstrip LN, and the Gram stain were 70, 48, 51, and 69%, respectively. There were 532 specimens with colony counts of >10(3) CFU/ml, and of these, the UTIscreen, the Bac-T-Screen, the Chemstrip LN, and the Gram stain detected 72, 81, 76, and 73%, respectively. Of the 249 probable pathogens isolated at >10(3) CFU/ml, the UTIscreen, the Bac-T-Screen, the Chemstrip LN, and the Gram stain detected 91, 95, 89, and 93%, respectively. The overall specificities at > 10(3) CFU/ml for these methods were 79, 55, 57, and 78%, respectively. The cost per test for detection was approximately $0.50 for the Chemstrip LN. Overall, the UTIscreen is rapid and easy to perform; its sensitivity compared favorably with those of the other screening methods; it had higher specificity than the Bac-T-Screen and Chemstrip LN; and it allowed for bathing of specimen.

Evaluation of BACTEC system for urine culture screening

We compared urine culturing performed by the calibrated loop method with a screening system (BACTEC). A total of 852 urine specimens were examined by both the conventional loop method and the BACTEC system. With the loop method, 193 (22.6%) urine samples were positive, whereas with the BACTEC system, 185 (21.7%) were positive (sensitivity, 96.01%). At a breakpoint of 10(4) CFU/ml, eight false-negatives were detected (sensitivity, 87.09%), and at a breakpoint of 10(5) CFU/ml, four false-negatives were observed (sensitivity, 97.6%). The specificity of the BACTEC system was 100%. We propose the BACTEC method as an effective alternative to the other growth-dependent screening tests for bacteriuria.

Screening for bacteriuria with Clinitec-200

A method of testing for bacteriuria with multiple reagent strips for blood, nitrite, and leucocyte esterase was evaluated. Of 669 urine specimens tested, 267 were negative on the reagent strips and so would ordinarily be discarded, creating a reduction in the workload of culturing urine specimens of 40%. Thirteen of these were false negative results, however, which represented 10% of all the samples with definite bacteriuria. Additional time was required for the screening test which reduced potential savings in manpower. Overall, we found costs to be slightly increased. In our laboratory this screening test was not economic and would produce an unacceptable rate of false negative results.

Clinical relevance of culture versus screens for the detection of microbial pathogens in urine specimens

The use of screens to detect "significant levels" of pathogenic microorganisms in urine specimens offers the advantages of both rapidly reporting results and controlling costs. Many of these screens, however, are insensitive at microbial counts below 10(5) colony-forming units (CFU)/ml of urine. It is increasingly apparent that patients with almost any type of urinary tract infection (except for most patients who are asymptomatic or who have pyelonephritis) may have urine concentrations of pathogens as low as 10(2) to 10(3) CFU/ml. This review documents factors that can contribute to diminished concentrations of microorganisms in urine, lists patient populations in whose urine microorganisms in concentrations well below 10(5) CFU/ml have been associated with infection, and makes recommendations for selection of laboratory tests, including rapid screens, for the diagnosis and management of urinary tract infections.

Automated bacteriuria screening using the Berthold LB 950 luminescence analyser

The Berthold LB950 Automatic Luminescence Analyser was used to estimate bacterial adenosine triphosphate in urine. The system provided a rapid (15 min) and fully automated screening test for bacteriuria at the 10(5) CFU/ml level. Bioluminescence results for 1040 urines were compared with viable counts using two reference culture methods and frequency distributions of bacterial counts and adenosine triphosphate levels were calculated. With a specificity of 79% the automated method showed a sensitivity of 84% using a pour plate reference count and 91% using a standard loop reference count. When contaminated urines were excluded the sensitivity improved to 98%. The automated bioluminescence test, though expensive, was shown to work well with good quality specimens.

Role of screening tests in rapid testing

Screening tests have had a major role in the diagnostic microbiology laboratory during recent years. Many factors have contributed to the increased use of these methods. The primary factor is the need for rapid detection and identification of the etiologic agent in life-threatening infections, which include bacterial meningitis, infective endocarditis and septicemia, and pneumonia. Various direct screening methods are also available for eliminating negative specimens rapidly. These methods have had an impact on laboratory work flow and the outpatient population by eliminating the possibility of bacterial infections of the urinary, upper respiratory, and gastrointestinal tracts. Screening methods have also been applied to isolated colonies for the rapid differentiation and identification of certain groups of organisms. Finally, many of these screening methods have contributed to cost-savings for both the laboratory and the patient. In this era of prospective pricing, and until the entrance of biotechnology into the diagnostic microbiology laboratory, the microbiologist must rely upon these rapid, inexpensive screening procedures. The role of these screening tests in the diagnostic microbiology laboratory and their impact on patient care and cost are reviewed herein.