Self-sampling of capillary blood for serological testing of SARS-CoV-2 by COVID-19 IgG ELISA

Brown, L.; Byrne, R. L.; Fraser, A.; Owen, S. I.; Cubas Atienzar, A. I.; Williams, C.; Kay, G. A.; Cuevas, L. E.; Fitchett, J. R. A.; Fletcher, T.; Garrod, G.; Kontogianni, K.; Krishna, S.; Menzies, S.; Planche, T.; Sainter, C.; Staines, H. M.; Turtle, L.; Adams, E. R.

Serological testing is emerging as a powerful tool to progress our understanding of COVID-19 exposure, transmission and immune response. Large-scale testing is limited by the need for in-person blood collection by staff trained in venepuncture. Capillary blood self-sampling and postage to laboratories for analysis could provide a reliable alternative. Two-hundred and nine matched venous and capillary blood samples were obtained from thirty nine participants and analysed using a COVID-19 IgG ELISA to detect antibodies against SARS-CoV-2. Thirty seven out of thirty eight participants were able to self-collect an adequate sample of capillary blood ([≥]50 l). Using plasma from venous blood collected in lithium heparin as the reference standard, matched capillary blood samples, collected in lithium heparin-treated tubes and on filter paper as dried blood spots, achieved a Cohen's kappa coefficient of >0.88 (near-perfect agreement). Storage of capillary blood at room temperature for up to 7 days post sampling did not affect concordance. Our results indicate that capillary blood self-sampling is a reliable and feasible alternative to venepuncture for serological assessment in COVID-19.