A pilot evaluation of whole blood finger-prick sampling for point-of-care HIV viral load measurement: the UNICORN study

Abstract

There is a global need for HIV viral load point-of-care (PoC) assays to monitor patients receiving antiretroviral therapy. UNICORN was the first study of an off-label protocol using whole blood finger-prick samples tested with and without a simple three minute spin using a clinic-room microcentrifuge. Two PoC assays were evaluated in 40 HIV-positive participants, 20 with detectable and 20 with undetectable plasma viral load (pVL) (<20 copies/ml). Using 100 µl finger-prick blood samples, the Cepheid Xpert HIV-1 Viral Load and HIV-1 Qual cartridges were compared with laboratory pVL assessment (TaqMan, Roche). For participants with undetectable viraemia by TaqMan, there was poor concordance without centrifugation with the TaqMan platform with only 40% 'undetectable' using Xpert VL and 25% 'not detected' using the Qual assay. After a 3 minute spin, 100% of samples were undetectable using either assay, showing full concordance with the TaqMan assay. Defining a lower limit of detection of 1000 copies/ml when including a spin, there was 100% concordance with the TaqMan platform with strong correlation (rho 0.95 and 0.94; p < 0.0001 for both assays). When including a simple microcentrifugation step, finger-prick PoC testing was a quick and accurate approach for assessing HIV viraemia, with excellent concordance with validated laboratory approaches.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1

Concordance between Roche TaqMan and GeneXpert assays. Percentages of samples reported ‘detected’ or ‘not detected’ using the qualitative Xpert HIV-1 Qual (a,b) and quantitative HIV-1 Viral Load cartridges (c,d), with and without incorporating a 3 minute centrifugation step from a 100 µl whole blood finger-prick sample. Panels a. and c. show participants with undetectable plasma viraemia using the Roche TaqMan assay tested using whole blood finger-prick samples using the GeneXpert Qual and Viral Load cartridges, respectively. Panels b and d show participants with detectable viraemia using the Roche TaqMan assay tested using the Qual and Viral Load cartridges, respectively. Arrows indicate the impact of introducing a 3 minute centrifugation ‘spin’ step to the protocol.

Figure 2

Impact of benchtop centrifugation on PoC finger-prick viral load quantification. Comparison of Roche TaqMan pVL assay with GeneXpert Viral Load assay without (a) or with (b) a 3 minute centrifugation step. Vertical line in (a) shows suggested lower limit of detection for the finger-prick protocol (1000 copies/ml) based on this study. Correlation between Roche TaqMan pVL assay and Xpert Viral Load assays when a lower limit of detection of 1000 copies/ml was imposed and 6 samples with pVL below this excluded (d). Values are Spearman’s Rho and P values. Bland Altman analysis comparing the Roche TaqMan with Xpert VL assay with centrifugation for samples > 1000 copies/ml (d).