This is a summary, written by members of the CITF Secretariat, of:

Nikiforuk AM, McMillan B, Bartlett SR, Márquez AC, Pidduck T, Kustra J, Goldfarb DM, Barakauskas V, Sinclair G, Patrick DM, Sadarangani M, Ogilvie GS, Krajden M, Morshed M, Sekirov I, Jassem AN. Performance of Immunoglobulin G Serology on Finger Prick Capillary Dried Blood Spot Samples to Detect a SARS-CoV-2 Antibody Response. Microbiol Spectr. 2022 Mar 10:e0140521. doi: 10.1128/spectrum.01405-21.

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

In a study now published in Microbiology Spectrum, a team of Vancouver investigators, led by Dr. Agatha Jassem of the British Columbia Center for Disease Control (BCCDC) and partially funded by the CITF, demonstrated that dried blood spot (DBS) testing should be considered reliable in detecting SARS-CoV-2 seropositivity acquired from both natural infection and vaccination.

The research team assessed the diagnostic accuracy of finger-prick capillary DBS samples to detect SARS-CoV-2 nucleocapsid (N), spike (S), and receptor binding domain (RBD) antibodies after infection and/or vaccination.

Key findings:

  • DBS analysis from an unvaccinated population possessed a sensitivitySensitivity is a metric defining a test’s capacity to correctly identify people that are infected with SARS-CoV-2 when a test is positive. For example, a test with a sensitivity of 79% will, on average, correctly identify 79 people in every 100 who are truly infected with SARS-CoV-2. of 79% and a specificitySpecificity is a metric defining a test’s capacity to correctly identify people that are not infected with SARS-CoV-2 when a test is negative. For example, a test with a specificity of 97% will, on average, correctly identify 97 people in every 100 who are truly not infected with SARS-CoV-2. of 97%. It was also found that DBS samples accurately detect SARS-CoV-2 seroconversion Seroconversion is the process by which antibodies are detected in the blood following exposure to a virus. 88% of the time.
  • Samples were collected 3 to 6 weeks after the administration of a first or second dose of COVID-19 vaccine. Comparing one with two doses increased the sensitivity of DBS testing to 97% and 100%, respectively. The increased sensitivity indicates that DBS testing will work well in a vaccinated population.
  • Predictive modelling done in a population of 10,000 shows that the predictive value of DBS testing changes in response to the prevalence of seroconversion. The test will perform optimally to quantify SARS-CoV-2 antibodies in a well vaccinated population.

These results are useful because DBS samplingThe participant is asked to follow a step-by-step process which involves them pricking their finger and depositing several blood drops onto a card which is then mailed back to a laboratory for analysis. Please see a video made by one of our funded studies here. eliminates the need for trained medical personnel since samples are self-collected; this is therefore a more feasible method for community collection of blood samples. In addition, collection cards are stable at ambient temperature for up to two weeks, simplifying transport. As observed with this study, tests performed on these types of samples characteristically exhibit high specificity and lower sensitivity, in part due to the low volume of sample collected (2-3 drops) and variations in collection practices. The comparable diagnostic accuracy of DBS to serum samples drawn by venipuncture, simpler collection requirements and a wider population reach, make serological testing from finger prick DBS a viable option in strategies to understand and combat the spread of SARS-CoV-2.

The study involved 6,841 participants throughput 2020-2021 in British Columbia. DBS and traditional venipuncture samples were obtained from 642 participants prior to vaccination and analysis was done to establish signal thresholds and calculate diagnostic accuracy. The researchers tested DBS samples with Meso Scale Discovery’s quantitative multiplex anti-IgG electrochemiluminescence assay (DBS-MSD).