“We believe that the antibodies that we’re detecting do confer some level of protection, but we want to know how much and how long that protection lasts”
-ABC News

Dr. Aneesh Mehta, Emory Vaccine Center

All lateral flow assay (LFA) tests, including ours, are operating under emergency use authorization (EUA) for diagnosis of SARS-CoV-2,15 allowing nucleic acid detection and immunoassay tests to be offered based on manufacturer-reported data without formal FDA clearance, that was issued on February 4, 2020, by the Secretary of the United States Department of Health and Human Services.

In general, test performance of kits that use a finger stick (lateral flow assays) have lower performance characteristics than those that use a full tube of blood, but finger stick assays allow reporting of results within 15 minutes compared to days for full tube assays sent to central labs for processing. High specificity testing is crucial in low-prevalence settings like the current COVID pandemic represents because even a low rate of false positives could overwhelm the number of true positive cases. However, as demonstrated below, our test kit has 100% specificity for anti-COVID 19 IgG, making our test kit a reasonable option for those who want a hassle-free testing experience yielding immediate results, compared to using a national central lab option for testing.

Complicating matters, there is no “gold standard” to identify true seropositive blood samples and therefore calculate a true test “sensitivity”. Researchers use serum samples from patients who previously tested positive for the COVID virus using the genetic test, and who had symptomatic disease, as likely “true positive” samples with which to test various test kit performance. However, the extent and time-course of antibody development after COVID 19 infection are not fully understood as yet, and may vary between different populations, even among RT- PCR-confirmed cases.

Therefore, focusing on the percent positivity by time interval after presentation of a symptomatic COVID infection, rather than the “sensitivity” of any assay is more practical and meaningful. High rates of positive results have not been typically reached until at least 2 weeks after clinical illness begins.

For our test, the majority of samples >20 days post-symptom onset had detectable anti-SARS-CoV-2 antibodies, suggesting good to excellent sensitivity in patients three or more weeks into their disease course. In one study posted on https://covidtestingproject.org , 10/11 (90.91%) patients tested positive for IgM and/or IgG >20 days after COVID symptoms began utilizing our assay. Test results in patients who were more recently infected with COVID 19 (less than 3 weeks before being tested) were more variable. Patients with positive tests should consider repeat testing using a different test platform to confirm their results. More importantly in this low-prevalence setting, specificity was 100% for IgG, with 0 out of 108 blood donor plasma specimens collected before July 2018, before COVID-19 existed, testing positive.

Currently, we have two different high quality LFA assays now in inventory, so anyone who tests positive with us will be retested with the other manufacturer’s test kit to confirm results. Also, anyone who has had a documented positive COVID 19 virus test positive result in the past, who can provide us with a copy of their positive test results, and who tests negative with us, will immediately be retested with the other manufacturer’s test to confirm negative results under these circumstances, at no extra charge in either case. This is a very valuable benefit that no one else will be offering and addresses all the noise in the media about unreliable test results. By adding the second test to confirm the first test results, we gain a “force multiplier effect” so that the combined PPV (positive predictive value) is 100% and the NPV (negative predictive value) is 99.9%.

For those who do test positive with our test, or other antibody tests, we still do not know the extent to which positive results by serology reflect a protective immune response although it is likely that IgG antibodies would confer some protection against repeat COVID infection.