UC Berkeley

The limiting antigen (LAg)-avidity assay is a serologic assay used for cross-sectional HIV incidence testing. We compared the results obtained with the LAg-avidity assay using dried blood spot (DBS) samples stored at room temperature (18°C-25°C) or stored frozen at -80°C with results obtained from matched plasma samples. Matched DBS and plasma samples (306 paired samples) were collected in the HIV Prevention Trials Network (HPTN) 068 trial in South Africa (2012-2014). The DBS were stored at room temperature before testing. Matched DBS and plasma samples (100 paired samples) from the Consortium for the Evaluation and Performance of HIV Incidence Assays (CEPHIA) were collected in 2016 and were stored at -80°C. All DBS testing was performed in 2017. Differences in normalized optical density (ODn) were compared between matched DBS and plasma samples. For DBS samples stored at room temperature (HPTN 068), the average difference in ODn values for plasma versus DBS was 1.49 (95% confidence intervals [CI]: 1.36-1.62). In contrast, when DBS samples were stored at -80°C (CEPHIA), the average difference in ODn values for plasma versus DBS was -0.22 (95% CI: -0.32 to -0.13). DBS samples stored at room temperature should not be used for cross-sectional HIV incidence testing with the LAg-avidity assay.