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Classification of HIV-1 virological treatment failure using the Roche cobas plasma separation card on cobas 8800
Lucia Hans1, Ed G Marins2, Christian O Simon2
1University of the Witwatersrand, School of Pathology, Department of Molecular Medicine and Haematology, Johannesburg, South Africa; National Health Laboratory Service, Johannesburg, South Africa.
Background:
Measurement of HIV-1 viral load (VL) is essential for monitoring antiretroviral treatment (ART) efficacy. In remote settings, dried blood spots (DBS) may be used as the specimen type. However, cellular components in DBS not present in the gold standard specimen type, plasma, may result in low specificity i.e., over-estimation of VL results from DBS compared to plasma. The Abbott RealTime HIV-1 assay system has been reported to have improved specificity using DBS compared to other tests. A new specimen collection matrix, the cobas plasma separation card (PSC, Roche Molecular Systems), enables specimen collection from a finger prick or venous blood, using a multi-layer absorption and filtration design that results in a specimen similar to plasma.
Objectives And Study Design:
We performed a direct comparison between VL results from PSC tested with the cobas 6800/8800 assay (c8800) and DBS tested with the Abbott RealTime HIV-1 assay.
Results:
Overall concordance between PSC and plasma around the 1000 copies/mL threshold was high (>97%). Compared to VL measured using DBS and the RealTime assay, PSC and c8800 showed improved sensitivity (96.9% vs 90.6%) and specificity (97.4% vs. 87.2%) using plasma as the reference, as there were fewer patients with VL below 1000 copies/mL in plasma in whom VL was over this threshold using PSC compared to DBS. The limit of detection for PSC was lower than for DBS (575 vs. 2314 copies/mL).
Conclusions:
cobas PSC represents a promising specimen type for use with the cobas 6600/8800 system in settings where plasma cannot be used.
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