The authors have read the journal’s policy and have the following competing interests: ANH received grant funding from Tasso, Inc. EB is a co-founder and employee of Tasso and holds equity stock. EW is an employee of Tasso and holds equity stock. BQ is an employee of Tasso and holds equity stock. This does not alter our adherence to PLOS ONE policies on sharing data and materials. There are no patents, products in development or marketed products associated with this research to declare. All other authors have no competing interests.
Efforts to minimize COVID-19 exposure during the current SARS-CoV-2 pandemic have led to limitations in access to medical care and testing. The Tasso-SST kit includes all of the components necessary for remote, capillary blood self-collection. In this study, we sought to investigate the accuracy and reliability of the Tasso-SST device as a self-collection device for measurement of SARS-CoV-2 IgG antibodies.
Capillary blood was obtained via unsupervised and supervised application of the Tasso-SST device, and venous blood was collected by standard venipuncture. Unsupervised self-collected blood samples underwent either extreme summer or winter-simulated shipping conditions prior to testing. Sera obtained by all three methods were tested concurrently using the EuroImmun anti-SARS-CoV-2 S1 IgG assay in a CLIA-certified clinical laboratory.
Successful Tasso-SST capillary blood collection by unsupervised and supervised administration was completed by 93.4% and 94.5% of participants, respectively. Sera from 56 participants, 55 with documented (PCR+) COVID-19, and 33 healthy controls were then tested for anti-SARS-CoV-2 IgG antibodies. Compared to venous blood results, Tasso-SST-collected (unstressed) and the summer- and winter-stressed blood samples demonstrated Deming regression slopes of 1.00 (95% CI: 0.99–1.02), 1.00 (95% CI: 0.98–1.01), and 0.99 (95% CI: 0.97–1.01), respectively, with an overall accuracy of 98.9%.
Capillary blood self-collection using the Tasso-SST device had a high success rate. Moreover, excellent concordance was found for anti-SARS-CoV-2 IgG results between Tasso-SST capillary and standard venous blood-derived sera. The Tasso-SST device should enable widespread collection of capillary blood for testing without medical supervision, facilitating epidemiologic studies.
The global SARS-CoV-2 pandemic has forced large numbers of people into various degrees of physical isolation and quarantine, increasing barriers to health care, laboratory testing, and epidemiological surveillance [
The Tasso-SST kit contains all the necessary components for an in-home capillary blood draw, including instructions, shipping materials, and a self-use blood collection device. The device includes an adhesive strip for attaching the device to the upper arm, a lancet assembly triggered by a large red button, and a collection tube with a separator gel designed to collect up to approximately 600 μL of capillary blood (
We describe our single-center experience using the Tasso-SST capillary blood collection device among volunteers and persons recovered from virologically documented COVID-19. We evaluated the success of obtaining blood for testing using the Tasso-SST device, either supervised or unsupervised. We then compared antibody levels detected in capillary blood obtained using the Tasso-SST device with venous blood obtained by standard venipuncture. Finally, capillary blood obtained via the Tasso-SST device was subjected to extreme temperature conditions that could potentially occur with shipping to evaluate the effects on antibody test results.
Male and female participants, ages 21 through 73, underwent University of Washington IRB-approved (#4312) written informed consent and study procedures at the University of Washington Virology Research Clinic in Seattle, WA between June and August 2020. Participants with documented evidence (serologic or RT-PCR) of prior SARS-CoV-2 infection who had been recruited as potential therapeutic plasma donors were enrolled in the current study; subjects must have been asymptomatic, afebrile for 14 or more days, be 28 days past the resolution of their COVID-19 illness, and were eligible to become a donor if their anti-SARS-CoV-2 neutralizing antibody titer was at least 1:80. Subjects must have met FDA-approved criteria per local blood collector for plasmapheresis, and be judged to have adequate peripheral venous access for plasmapheresis donation. Healthy controls included male and female participants, ages 25 through 69, recruited between June and August 2020. These participants were required to have no known history of COVID–19 illness. Green’s rule of thumb calculation for a linear regression (m = 1) for medium effect size yielded a sample size of 58 [
Capillary blood specimens were collected with the Tasso-SST blood sampling kit (Tasso, Inc., Seattle, WA). The study design and flow of samples is outlined in
Two of 91 subjects were excluded due to inability to obtain blood samples; 56 convalescent and 33 healthy subjects had blood samples tested.
Serologic testing was performed using an FDA-authorized (EUA), CE-marked EuroImmun (Germany) anti-SARS-CoV-2 IgG kit [
Statistical analyses were performed using GraphPad Prism software version 9.0.0 (San Diego, CA) and R version 3.4.4 [
The characteristics of the 89 participants whose samples underwent Anti-SARS-CoV-2 IgG testing are outlined in
Characteristic | Numbers |
---|---|
Median Age (Range) | 45 (21–73) |
Male Gender (%) | 30 (33.7) |
White (%) | 68 (76.4) |
Asian (%) | 11 (12.4) |
Black (%) | 5 (5.6) |
Hispanic (%) | 7 (7.9) |
Any college education & above (%) | 85 (95.5) |
Technical/trade school (%) | 4 (4.5%) |
Median Days Since PCR+ (Range) |
96 (36–128) |
Sample collection was attempted from 91 participants enrolled in the study (
Blood Draw Method | Successful |
Redraw Required |
Unsuccessful |
---|---|---|---|
Venous Draw | 90 (98.9) | 1 (1.1) | 1 |
Tasso–Administered Draw | 86 (94.5) | 5 (5.5) | 1 |
Tasso–Self Draw | 85 (93.4) | 6 (6.6) | 0 |
The distribution of anti-SARS-CoV-2 IgG results according to the method of sample collection and handling is shown in
Interpretation | EuroImmun Thresholds | Venous Blood, N | Tasso-Unstressed, N | Tasso- Stressed |
---|---|---|---|---|
Negative | <0.8 | 40 | 41 | 41 |
Borderline | ≥0.8<1.1 | 1 | 0 | 0 |
Positive | ≥1.1 | 48 | 48 | 48 |
aTasso-Stressed includes summer and winter conditions combined; the one discordant sample was winter-stressed
The pair-wise correlation between the OD ratios obtained after blood collection by standard venipuncture and Tasso-SST devices is shown in
Each circle represents results from an individual participant. Correlation between EuroImmun OD ratios from venous blood and provider-administered Tasso device collected capillary blood (Tasso Unstressed (TU), N = 89, p<0.0001, Deming regression: Y = 1.00*X—0.04) (A). Correlation between venous samples results and those from stressed Tasso-SST (TS) samples under summer (B, N = 44, p<0.0001, Deming regression: Y = 1.00 *X– 0.03) or winter conditions (C, N = 45, p<0.0001, Deming regression: Y = 0.99*X– 0.03).
The self-collected Tasso-SST samples underwent a 48-hour shipping simulation as described in Materials and Methods. Anti-SARS-CoV-2 IgG results from both summer- (N = 44) and winter-stressed samples (N = 45) were compared to venous samples that underwent routine processing procedures after collection (
We investigated the performance of a capillary blood collection device intended for self-application and shipping to a clinical laboratory for subsequent anti-SARS-CoV-2 S1 IgG antibody testing. Our findings indicated that the Tasso-SST device was used successfully to collect adequate volume for testing by a manual ELISA 93.4% of the time, compared to 98.9% for venous blood draw by a trained professional. Moreover, we showed that quantitative antibody levels detected in the venous and Tasso-SST capillary serum were highly correlated, even when the samples were stressed by winter and summer conditions (to mimic extreme shipping conditions) compared to clinic-obtained venous blood samples that were promptly delivered to the laboratory.
The window of time between PCR-positivity and anti-Spike IgG testing in our study was relatively narrow at 36–128 days. However, the EuroImmun anti-Spike assay results from blood collections during this interval encompassed a relatively broad range of OD ratio values (0.05 to 10.8 OD ratios) for the 89 enrolled subjects. While higher antibody levels may be present earlier after infection among hospitalized patients compared to the outpatients we tested, it is unlikely that the Tasso device would be utilized in that population. The most relevant concern would be the correlation between antibody levels in venous and capillary blood at lower levels; half of the samples we tested yielded results between 0.2 and 5.4, which encompasses both low-positive and negative values. The excellent correlation between results from venous and capillary blood provide confidence that the material type collected via Tasso will allow for the accurate measurement of low antibody levels using high quality EUA SARS-CoV-2 ELISAs.
Unsupervised self-collection of blood samples at home has several potential limitations. One potential limitation is the need for adequate education of patients so that the device is correctly applied and samples shipped to the laboratory. In our study, 94.9% of participants successfully self-collected capillary blood; the high educational attainment of our cohort may have contributed to the high success rate. Outside of the current study, Tasso, Inc. evaluated an additional 20 individuals who had no prior experience with sample self-collection; 13 had attended “some college”, 3 had attended a trade or technical school, and 3 were high school graduates. Among these 20 subjects, 17 (85%) were able to successfully self-collect an acceptable sample on their first attempt following the kit instructions for performing the collection.
Other potential limitations include the time needed for shipping prior to specimen processing (resulting in a delay of testing) and potential adverse environmental (or climatic) conditions associated with shipping that could affect the stability of the analyte to be tested. However, as shown here, antibodies tend to be stable analytes; the mean elapsed time between Tasso sample collection and processing was 72.7 hours, a relatively long period of time. Hodgkinson and colleagues also evaluated the effect of delayed processing and temperature on results from a multiplex immunoassay measuring antibodies against various infectious antigens and found their results to be stable at room temperature through 6 days [
A final limitation of this self-collection approach is the volume of blood that can be obtained using the Tasso-SST device. In the current study, the average whole blood volume obtained by Tasso-SST self-collection was 339 μL, which corresponds to approximately 196 μL of serum. Consequently, 93.4% of samples had sufficient volume for testing by our manual ELISA, which required only 10 μL. While this small sample volume is typical of manual ELISAs, the overall volume limitation could be an issue for analytes measured using automated instruments, since they typically require larger serum volumes for testing.
An alternative approach to remote blood collection for subsequent laboratory testing is the use of dried blood spots (DBS) [
The current global pandemic has led to restricted movement and gathering of people to mitigate the spread of viral infection. In this setting, telemedicine has emerged as an increasingly common alternative to in-person medical visits [
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The authors wish to thank the members of the University of Washington Clinical Immunology Laboratory for conducting the testing, Michael Walker and Jing Shi for help with statistical analyses, and the study participants for donating their time and samples for this study.