Dried blood spot sampling potential for COVID-19 antibody testing

Using dried blood spot samples is an accurate alternative to venous blood in detecting SARS-CoV-2, the virus that causes the novel coronavirus (COVID-19), antibodies, according to new research by immunology experts at the University of Birmingham published in the journal in Emerging Infectious Diseases.

Currently, antibody testing for COVID-19 uses serum or plasma, which requires a full intravenous blood sample collected by a trained phlebotomist. For population-wide or high-volume testing, the use of such sampling is limited by logistic challenges, resources, and costs, as well as the risk of SARS-CoV-2 exposure from direct patient contact, the researchers said in a statement.

The researchers analyzed serum and dried blood spot samples from volunteers, some of whom had previously tested positive for SARS-CoV-2 by molecular tests, while the status of other volunteers was either negative or unknown. The anonymized matched serum and dried blood spot samples were then processed using a highly sensitive enzyme-linked immunosorbent assay (ELISA) test, which specifically detects antibodies, IgG, IgA, and IgM, to the SARS-CoV-2 trimeric spike protein, according to the research.

The results showed a significant correlation between matched dried blood spot and serum samples, with minimal differences in results observed by sample type and negligible discordance. Relative to serum samples, dried blood spot samples achieved 98 percent sensitivity and 100 percent specificity for detecting anti-SARS-CoV-2 S glycoprotein antibodies. Additionally, 100 percent of the PCR-positive samples were also antibody-positive in dried blood spots.

 Dried blood spot sampling is simple, inexpensive, and can be self-collected by the patient at home, using a finger prick, the researchers said. The sample can then be collected on a forensic grade card before being posted back to labs for processing. This offers possibilities to widen access to antibody testing, particularly in more resource-limited countries.

"Our results have demonstrated that dry blood spot sampling not only offers a viable alternative for antibodies testing, but one that overcomes the limitations that current methods can present by eliminating the need for skilled phlebotomists,” said Matthew O’Shea, MBChB, MRCP, FRCPath, DPhil (Oxon), DTM&H, senior author, in a statement. “[Dried blood spot sampling] offers the opportunity for wider population-level testing and improved surveillance in vulnerable groups such as patients with chronic conditions, the immunocompromised, and the elderly by removing the need to come into contact with a healthcare professional during sample collection."

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