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Improved sensitivity of the urine CAA lateral-flow assay for diagnosing active Schistosoma infections by using larger sample volumes.

Corstjens PL, Nyakundi RK, de Dood CJ, Kariuki TM, Ochola EA, Karanja DM, Mwinzi PN, van Dam GJ - Parasit Vectors (2015)

Bottom Line: Only a single 2 mL urine sample is needed, but analysing larger sample volumes could still increase test accuracy.The UCAA2000 test is an appropriate candidate for accurate identification of all infected individuals in low-endemic regions.Assay materials do not require refrigeration and collected urine samples may be stored and transported to central test laboratories without the need to be frozen.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Cell Biology, Leiden University Medical Center, Einthovenweg 20, P.O. Box 9600, 2300 RC, Leiden, the Netherlands. p.corstjens@lumc.nl.

ABSTRACT

Background: Accurate determination of Schistosoma infection rates in low endemic regions to examine progress towards interruption of transmission and elimination requires highly sensitive diagnostic tools. An existing lateral flow (LF) based test demonstrating ongoing infections through detection of worm circulating anodic antigen (CAA), was improved for sensitivity through implementation of a protocol allowing increased sample input. Urine is the preferred sample as collection is non-invasive and sample volume is generally not a restriction.

Methods: Centrifugal filtration devices provided a method to concentrate supernatant of urine samples extracted with trichloroacetic acid (TCA). For field trials a practical sample volume of 2 mL urine allowed detection of CAA down to 0.3 pg/mL. The method was evaluated on a set of urine samples (n = 113) from an S. mansoni endemic region (Kisumu, Kenya) and compared to stool microscopy (Kato Katz, KK). In this analysis true positivity was defined as a sample with either a positive KK or UCAA test.

Results: Implementation of the concentration method increased clinical sensitivity (Sn) from 44 to 98% when moving from the standard 10 μL (UCAA10 assay) to 2000 μL (UCAA2000 assay) urine sample input. Sn for KK varied between 23 and 35% for a duplicate KK (single stool, two slides) to 52% for a six-fold KK (three consecutive day stools, two slides). The UCAA2000 assay indicated 47 positive samples with CAA concentration above 0.3 pg/mL. The six-fold KK detected 25 egg positives; 1 sample with 2 eggs detected in the 6-fold KK was not identified with the UCAA2000 assay.

Conclusions: Larger sample input increased Sn of the UCAA assay to a level indicating 'true' infection. Only a single 2 mL urine sample is needed, but analysing larger sample volumes could still increase test accuracy. The UCAA2000 test is an appropriate candidate for accurate identification of all infected individuals in low-endemic regions. Assay materials do not require refrigeration and collected urine samples may be stored and transported to central test laboratories without the need to be frozen.

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Related in: MedlinePlus

Expected qualitative UCAA2000 test results for samples tested with UCAA10 and UCAA250. The Kisumu sample set (n = 113) was tested with both the UCAA10 and UCAA250 assay. Only a non-random subset (n = 73; selection based on UCAA10/250 results) was tested with the UCAA2000 assay. The subset included 52 samples with a negative UCAA250 result. Ten samples with a positive test result for both UCAA10 and UCAA250, plus 30 samples with a negative test result for the UCAA250 were excluded. Extrapolation: for the 30 negatives, the same percentage of positives (21%) was assumed as empirically determined for the 52 negatives tested with the UCAA2000 assay. Numbers between brackets indicate samples with a negative test result; (+) and (−) following the UCAA assay indicate a positive or negative test result, respectively.
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Fig4: Expected qualitative UCAA2000 test results for samples tested with UCAA10 and UCAA250. The Kisumu sample set (n = 113) was tested with both the UCAA10 and UCAA250 assay. Only a non-random subset (n = 73; selection based on UCAA10/250 results) was tested with the UCAA2000 assay. The subset included 52 samples with a negative UCAA250 result. Ten samples with a positive test result for both UCAA10 and UCAA250, plus 30 samples with a negative test result for the UCAA250 were excluded. Extrapolation: for the 30 negatives, the same percentage of positives (21%) was assumed as empirically determined for the 52 negatives tested with the UCAA2000 assay. Numbers between brackets indicate samples with a negative test result; (+) and (−) following the UCAA assay indicate a positive or negative test result, respectively.

Mentions: Note that the subset of 73 samples does not represent an absolute random selection of the full Kisumu set. The subset did not include 30 out of 82 samples that had tested negative with the UCAA10 and UCAA250 assay. Also not included were 10 out of 21 positive samples that demonstrated high reactivity with both the UCAA10 and −250 assay and undoubtedly would return a positive test result with the UCAA2000 (Figure 4).Figure 4


Improved sensitivity of the urine CAA lateral-flow assay for diagnosing active Schistosoma infections by using larger sample volumes.

Corstjens PL, Nyakundi RK, de Dood CJ, Kariuki TM, Ochola EA, Karanja DM, Mwinzi PN, van Dam GJ - Parasit Vectors (2015)

Expected qualitative UCAA2000 test results for samples tested with UCAA10 and UCAA250. The Kisumu sample set (n = 113) was tested with both the UCAA10 and UCAA250 assay. Only a non-random subset (n = 73; selection based on UCAA10/250 results) was tested with the UCAA2000 assay. The subset included 52 samples with a negative UCAA250 result. Ten samples with a positive test result for both UCAA10 and UCAA250, plus 30 samples with a negative test result for the UCAA250 were excluded. Extrapolation: for the 30 negatives, the same percentage of positives (21%) was assumed as empirically determined for the 52 negatives tested with the UCAA2000 assay. Numbers between brackets indicate samples with a negative test result; (+) and (−) following the UCAA assay indicate a positive or negative test result, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4418045&req=5

Fig4: Expected qualitative UCAA2000 test results for samples tested with UCAA10 and UCAA250. The Kisumu sample set (n = 113) was tested with both the UCAA10 and UCAA250 assay. Only a non-random subset (n = 73; selection based on UCAA10/250 results) was tested with the UCAA2000 assay. The subset included 52 samples with a negative UCAA250 result. Ten samples with a positive test result for both UCAA10 and UCAA250, plus 30 samples with a negative test result for the UCAA250 were excluded. Extrapolation: for the 30 negatives, the same percentage of positives (21%) was assumed as empirically determined for the 52 negatives tested with the UCAA2000 assay. Numbers between brackets indicate samples with a negative test result; (+) and (−) following the UCAA assay indicate a positive or negative test result, respectively.
Mentions: Note that the subset of 73 samples does not represent an absolute random selection of the full Kisumu set. The subset did not include 30 out of 82 samples that had tested negative with the UCAA10 and UCAA250 assay. Also not included were 10 out of 21 positive samples that demonstrated high reactivity with both the UCAA10 and −250 assay and undoubtedly would return a positive test result with the UCAA2000 (Figure 4).Figure 4

Bottom Line: Only a single 2 mL urine sample is needed, but analysing larger sample volumes could still increase test accuracy.The UCAA2000 test is an appropriate candidate for accurate identification of all infected individuals in low-endemic regions.Assay materials do not require refrigeration and collected urine samples may be stored and transported to central test laboratories without the need to be frozen.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Cell Biology, Leiden University Medical Center, Einthovenweg 20, P.O. Box 9600, 2300 RC, Leiden, the Netherlands. p.corstjens@lumc.nl.

ABSTRACT

Background: Accurate determination of Schistosoma infection rates in low endemic regions to examine progress towards interruption of transmission and elimination requires highly sensitive diagnostic tools. An existing lateral flow (LF) based test demonstrating ongoing infections through detection of worm circulating anodic antigen (CAA), was improved for sensitivity through implementation of a protocol allowing increased sample input. Urine is the preferred sample as collection is non-invasive and sample volume is generally not a restriction.

Methods: Centrifugal filtration devices provided a method to concentrate supernatant of urine samples extracted with trichloroacetic acid (TCA). For field trials a practical sample volume of 2 mL urine allowed detection of CAA down to 0.3 pg/mL. The method was evaluated on a set of urine samples (n = 113) from an S. mansoni endemic region (Kisumu, Kenya) and compared to stool microscopy (Kato Katz, KK). In this analysis true positivity was defined as a sample with either a positive KK or UCAA test.

Results: Implementation of the concentration method increased clinical sensitivity (Sn) from 44 to 98% when moving from the standard 10 μL (UCAA10 assay) to 2000 μL (UCAA2000 assay) urine sample input. Sn for KK varied between 23 and 35% for a duplicate KK (single stool, two slides) to 52% for a six-fold KK (three consecutive day stools, two slides). The UCAA2000 assay indicated 47 positive samples with CAA concentration above 0.3 pg/mL. The six-fold KK detected 25 egg positives; 1 sample with 2 eggs detected in the 6-fold KK was not identified with the UCAA2000 assay.

Conclusions: Larger sample input increased Sn of the UCAA assay to a level indicating 'true' infection. Only a single 2 mL urine sample is needed, but analysing larger sample volumes could still increase test accuracy. The UCAA2000 test is an appropriate candidate for accurate identification of all infected individuals in low-endemic regions. Assay materials do not require refrigeration and collected urine samples may be stored and transported to central test laboratories without the need to be frozen.

Show MeSH
Related in: MedlinePlus