Accuracy of calibrated-loop transfer

Albers, A C; Fletcher, Ronald D.

doi:10.1128/jcm.18.1.40-42.1983

Cited by 40 publications

(8 citation statements)

References 4 publications

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“…Apart from the performance characteristics linked to the calibration of the loop, many other variables may cause sampling errors. Less fluid is sampled when containers with small diameters are used, and a larger volume is sampled when the loop is inserted and withdrawn at a 45°angle or when the shank of the loop is immersed (1,2). Containers with small diameters may cause the loop to pick up a smaller volume since plastic-liquid (adhesive) forces are greater than liquid-liquid (cohesive) forces (1).…”

Section: Discussionmentioning

confidence: 99%

“…Less fluid is sampled when containers with small diameters are used, and a larger volume is sampled when the loop is inserted and withdrawn at a 45°angle or when the shank of the loop is immersed (1,2). Containers with small diameters may cause the loop to pick up a smaller volume since plastic-liquid (adhesive) forces are greater than liquid-liquid (cohesive) forces (1). When the shank of the loop is wetted by deep immersion into the fluid, excess liquid drains down and enlarges the volume transferred (2).…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Accuracy and Precision of Quantitative Calibrated Loops in Transfer of Bronchoalveolar Lavage Fluid

Jacobs¹,

Brauwer²,

Cornelissen³

et al. 2000

J. Clin. Microbiol.

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Quantitative cultures of bronchoalveolar lavage (BAL) fluid are important in the diagnosis of ventilatorassociated pneumonia, and calibrated loops are commonly used to set up these cultures. In this study, the performances of calibrated 0.010-and 0.001-ml loops in the transfer of BAL fluid were determined. Five loops of one lot from seven manufacturers were tested. Calibrations were performed by the gravimetric method (0.010-ml loops) and the colorimetric method (0.001-ml loops). Most of the 0.010-ml loops displayed a precision that was less than 10%, but six of them showed very poor accuracies as they transferred a deficiency (nichrome loops) or an excess (disposable loops) of BAL fluid that exceeded ؎10%. The mean maximum and minimum BAL fluid volumes delivered by the 0.010-ml loops differed by a factor 3. The 0.001-ml loops displayed acceptable precision. Five of them showed inaccuracies of <؎10%, and mean maximum and minimum BAL fluid volumes had a range of a factor of 2. For all loops, the volumes of BAL fluid sampled were larger than the volumes of reagent-grade water sampled. Results of the colony counting experiments confirmed these findings and revealed a high intra-assay variability for the 0.001-ml loops. We conclude that, when BAL fluid samples are cultured with calibrated loops, (i) proper verification of the calibration of these loops is mandatory, (ii) calibrations should be performed with BAL fluid as the test solution, and (iii) borderline quantitative culture results should be interpreted with knowledge of the inaccuracy values of these loops.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Accuracy and Precision of Quantitative Calibrated Loops in Transfer of Bronchoalveolar Lavage Fluid

Jacobs¹,

Brauwer²,

Cornelissen³

et al. 2000

J. Clin. Microbiol.

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“…A possible explanation for decreased specificities by the test methods is that low-level bacteriuria may not be detected by the culture method. Also, it has been reported that the culture method may have an error rate of as high as 50% (1). Another contributing factor may have been the presence of antimicrobial agents which inhibit microbial growth but do not inhibit detection by bioluminescence or filtration (6).…”

Section: Resultsmentioning

confidence: 99%

Rapid bioluminescence method for bacteriuria screening

et al. 1989

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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 >105 CFU/ml by the culture method. Of these, the UTIscreen detected 96% (265 of 276) using .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 >105 CFU/mI, 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 >105 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 > 105 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 >103 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 >103 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 >103 CFU/ml for these methods were 79, 55, 57, and 78%, respectively. The cost per test for detection was approximately $1.00 to $1.20 for the UTIscreen, the Bac-T-Screen, and the Gram stain and approximately $0.50 for the Chemstrip LN. Overall, the UTIscreen is rapid and easy to perform; its sensitivity compared favorably with those of other screening methods; it had a higher specificity than the Bac-T-Screen and Chemstrip LN; and it allowed for batching of specimens.

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“…Studies have indicated that the use of calibrated loops can be imprecise ( 3 ). Albers and Fletcher ( 8 ) noted that “the use of the calibrated loop by clinical microbiologists to determine colony counts from urine specimens is only semiquantitative and not very reliable, as the reproducibility of the method is dependent on many uncontrolled variables.” In an evaluation of the WASP instrument, Harrington and colleagues ( 9 ) noted that the colony counts produced by the WASP increased as the loops were inserted deeper into the specimen tube. This was most notable in this study with the WASP 1-μl loop.…”

Section: Discussionmentioning

confidence: 99%

“…We suspect that the relatively higher colony counts obtained with the WASP-1 and WASP-10 instruments compared to those with a calibrated pipette were due to the use of a wire loop to transfer the specimen from the transport tube to the agar plate. As noted by Albers and Fletcher ( 8 ), there are inherent inaccuracies associated with the use of a 1-μl loop. Importantly, the InoqulA and WASP instruments utilize different technologies to determine the depth of the liquid to which the transfer device (pipette versus loop) goes.…”

Section: Discussionmentioning

confidence: 99%

Comparative Evaluation of Inoculation of Urine Samples with the Copan WASP and BD Kiestra InoqulA Instruments

et al. 2016

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This study evaluated the quantitative results from and quality of the inoculation patterns of urine specimens produced by two automated instruments, the Copan WASP and the BD InoqulA. Five hundred twenty-six urine samples submitted in 10-ml canisters containing boric acid were processed within 30 min on an InoqulA instrument plating 10 μl of specimen, and on two WASP instruments, one plating 1 μl of specimen (WASP-1), and the second plating 10 μl of WASP (WASP-10). All samples were incubated, analyzed, and digitally imaged using the BD Kiestra total lab automation system. The results were evaluated using a quantitative protocol and assessed for the presence or absence of ≥5 distinct colonies. Separate studies were conducted using quality control (QC) organisms to determine the relative accuracy of WASP-1, WASP-10, and InoqulA instruments compared to the results obtained with a calibrated pipette. The results with QC organisms were calculated as the ratios of the counts of the automated instruments divided by the counts for the calibrated pipette (the gold standard method). The ratios for the InoqulA instrument were closest to 1.0, with the smallest standard deviations indicating that compared to a calibrated pipette, the InoqulA results were more accurate than those with the WASP instrument. For clinical samples, the WASP instruments produced higher colony counts and more commensals than the InoqulA instrument, with differences most notable for WASP-1. The InoqulA instrument was significantly better at dispersing organisms with counts of ≥105 bacteria/ml of urine than were the WASP-1 and WASP-10 instruments (P < 0.05). Our results suggest that the InoqulA quantitative results are more accurate than the WASP results, and, moreover, the number of isolated colonies produced by the InoqulA instrument was significantly greater than that produced by the WASP instrument.

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Accuracy of calibrated-loop transfer

Cited by 40 publications

References 4 publications

Accuracy and Precision of Quantitative Calibrated Loops in Transfer of Bronchoalveolar Lavage Fluid

Accuracy and Precision of Quantitative Calibrated Loops in Transfer of Bronchoalveolar Lavage Fluid

Rapid bioluminescence method for bacteriuria screening

Comparative Evaluation of Inoculation of Urine Samples with the Copan WASP and BD Kiestra InoqulA Instruments

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