A compelling alternative to dried blood spots - Pplasma separation card for the quantification of HIV-1 RNA viral load
Background: Plasma HIV viral load (VL) testing is the preferred means of monitoring response to antiretroviral treatment (ART) and programme performance. While Dried Blood Spots (DBS) hold considerable logistical advantages over plasma-based VL, performance based limitations still remain. DBS VL can lead to misclassifications of virological failure at 1000 cp/mL and have higher limits of detection (LOD) than plasma assays. We aim to evaluate the usability by health care workers (HCW) and analytical performance of a novel plasma separation card (PSC) versus plasma for the quantification of HIV-1 RNA.
Methods: HCW collected 140µL of finger-prick
capillary blood from ~50 HIV-infected patients and transferred to the PSC,
immediately after, venous EDTA whole blood was drawn by venipuncture. In
addition, residual venous EDTA whole blood from ~400 adult HIV-infected
patients was spotted onto PSC. We determined LOD using WHO International-Standard,
specificity and sensitivity at 1000 cp/mL and specimen stability at a range of
temperatures and storage durations in both COBAS®
Ampliprep COBAS TaqMan® (CAP/CTM)
and cobas® 8800 systems using the
PSC. PSC performance was assessed in relation to EDTA plasma in both assays.
Results: Overall HCW rated sample collection positively, the lancet was considered easy to use, as were the capillary tube and blood transfer to PSC. Of ~100 specimens with quantitative values in both PSC and plasma, the mean log10 difference between EDTA-plasma and PSC was 0.05 cp/mL (95%CI = -0.01 to 0.11). The LOD for cobas® HIV-1 was determined at 790.2 cp/mL and for CAP/CTM HIV-1 v2 737.9 cp/mL. At 1000 copies/mL, the sensitivity of PSC samples was 97.0% (128/132) and specificity 97.2% (343/353) for cobas® HIV-1 and showed an excellent correlation to plasma (Deming R2 = 0.90) over the linear range. PSC results were unaffected by different temperature and storage conditions (table1).
Conclusions: PSC collected samples are easy to prepare, correlate well with plasma VL and have demonstrated adequate sensitivity and specificity in a real world/clinical setting. The card provides an alternative sample collection to DBSs and, by minimising cell-associated viral nucleic acid contamination, leads to more accurate result. This PSC supports the 90-90-90 VL scale-up.
[Table 1: Analytical and clinical performance of Plasma separation card]
S. Carmona1,2, B. Seiverth3, D. Magubane2, L. Hans1,2, M. Hoppler3
1University of the Witwatersrand, Molecular Medicine and Haematology, Johannesburg, South Africa, 2National Health Laboratory Service, Johannesburg, South Africa, 3Roche Diagnostics International AG, Rotkreuz, Switzerland