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

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 μl). 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. ### Competing Interest Statement SK is a member of the Scientific Advisory Committee for the Foundation for Innovative New Diagnostics (FIND) a not for profit organisation that produces global guidance on affordable diagnostics. The views expressed here are personal opinions and do not represent the recommendations of FIND. ### Funding Statement This study was supported by the DFID/Wellcome Trust Epidemic Preparedness coronavirus grant (220764/Z/20/Z). ERA, LEC, TF and LT are funded by the Centre of Excellence in Infectious Diseases Research (CEIDR), the Alder Hey Charity and the National Institute for Health Research Health Protection Research Unit (NIHR HPRU) in Emerging and Zoonotic Infections (NIHR200907) at University of Liverpool (UoL) in partnership with Public Health England (PHE), in collaboration with Liverpool School of Tropical (LSTM) Medicine and the University of Oxford. ERA, LEC and TF are based at LSTM; LT is based at UoL. LT is supported by a Wellcome fellowship (grant number 205228/Z/16/Z). HMS is supported by the Wellcome Trust Institutional Strategic Support Fund (204809/Z/16/Z) awarded to St. George’s University of London. The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR, the Department of Health or Public Health England. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study was reviewed and approved by the National Health Service Research Ethics Committee Liverpool Central IRAS number 16/NW/0160. All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes Raw data were generated at Liverpool School of Tropical Medicine. Derived data supporting the findings of this study are available from the corresponding author ERA on request.