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Evaluation of the use of dried blood spots or dried plasma spots in combination with the Cavidi Exavir® Load RT Assay
Presented by Lisette Babette van Rooijen, Australia.
van Rooijen L.B.1, Morris L.1, Steele P.1, Greengrass V.1, Plate M.1, Crowe S.1
1Burnet Institute for Medical Research and Public Health, Clinical Research Laboratory, Melbourne, Australia
Objectives: The Cavidi ExaVir® Load assay is an alternative low cost HIV viral load assay, predominantly for the use in resource-constrained countries. This assay measures HIV reverse transcriptase (RT) activity and requires 1 ml pre-frozen plasma which is often not feasible in remote locations; therefore a practical, field-friendly and inexpensive method of blood collection and transport is required. We have evaluated dried blood and plasma spots (DBS/DPS) in combination with the Cavidi assay.
Methods: DBS/DPS were made by applying 50µl onto Whatman® No. 903 Protein Saver Cards. The spots were dried overnight and stored at room temperature (22-24°C) for 4-40 days. The spots (1 or 5 per test) were resuspended in 1 ml HIV negative plasma per spot and were agitated for the first incubation. Filter paper was then removed and the assay continued as per manufacturers instructions. The results were adjusted for volume.
Results: DBS/DPS were prepared from five patients with viral load between 37450-148100 copies/ml as determined by the Cavidi assay. Five DPS per test showed an average difference from the normal assay of -0.55log (-0.23 to -1.07, n=6), while the use of one DPS showed an average difference of -0.88log (-0.45 to -1.28, n=6). The use of five DBS per test showed an average difference of -1.85log (-1.25 to -2.52, n=3), while the use of one DBS per test showed an average difference of -1.24log (-1.03 to -1.44 n=3) from the normal assay. In total, 89% of spots tested gave detectable results (n=18); 100% of tests using five spots of blood or plasma were detected (n=9) while only 78% of tests using one spot gave detectable results (n=9).
Conclusions: These preliminary results show we were able to successfully recover and quantitate the RT enzyme from DBS/DPS with the Cavidi assay however; further optimization and validation of this method is required.
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