COVID-19 Antigen Test Devices

The federal Department of Health and Human Services announced last week a plan to provide a point-of-care testing device-the Quidel Sofia or Sofia 2 Instruments or the BO Veritor Plus System- and associated test kits to all skilled nursing facilities (in possession of a CUA waiver, which includes Deerfield) across the nation. Shipments of the devices to 2,000 nursing homes in COVID-19 hotspots are set to begin as early as this week, with other skilled nursing facilities to receive their devices at some unspecified point thereafter. Purportedly, along with the testing device itself, enough (device-specific) test kits will be provided to accommodate point prevalence surveillance of all healthcare personnel and Skilled Nursing residents for 4 weeks. What’s interesting about the Quidel Sofia versions 1 and 2 and the BD Veritor Plus is that they are antigen tests. Two different types of COVID-19 tests exist: diagnostic tests and antibody tests.

Diagnostic Tests
An invaluable tool in infectious disease containment, the goal of diagnostic testing is to determine if an individual has active SARS-CoV2 (novel coronavirus) infection (COVID- 19). These tests have practicality for individuals displaying signs or symptoms consistent with COVID-19, individuals who have had exposures to COVID-19, and individuals undergoing surveillance testing for active COVID-19 infection for any reason. Currently, there are two distinct types of diagnostic tests for COVID-19:

• Molecular Tests
In the case of COVID-19, a molecular test called a RT-PCR is the current gold standard for diagnosis of this disease. Like all molecular tests, the RT-PCR (real time, reverse transcription polymerase chain reaction) detects SARS-CoV2 genetic material (nucleic acid) within a specimen. Specimens are collected by swabbing the nasal passages or throat, and most test results are available within 24 hours to a week or more, depending upon the laboratory (though a few rapid molecular tests are available that are capable of delivering same-day results). RT-PCR tests offer the highest degree of sensitivity among COVID-19 diagnostic tests (lowest risk for false negative results; the risk for false negative results with RT-PCR does remain unsettlingly high, but this is most often due to improperly collected or stored specimens rather than test insensitivity) and an excellent degree of specificity (meaning that a positive result is definitive).

• Antigen Tests
An antigen test detects specific proteins located on the surface of the virus. Test specimens are collected by swabbing the nasal passages or throat and results are generally available within an hour. If you’ve ever had an in-office, rapid test for influenza or strep throat, you’ve benefitted from antigen testing technology. Antigen testing offers excellent specificity (meaning that a positive result is essentially definitive} but a concerning degree of sensitivity (with up to 20% of tests of properly obtained specimens falsely resulting negative, even in devices authorized by the FDA for emergency use}. The insufficient sensitivity of this testing method necessitates a confirmatory RT-PCR when SARS-CoV2 antigen testing reveals preliminary negative results in a person displaying symptoms of COVID-19 or with known exposure to the virus.

Antibody Tests
When a human is exposed to a pathogen (a novel coronavirus, for example}, a healthy immune system responds to the threat by rapidly producing and deploying a protein called an antibody that is specific to the target pathogen. Antibodies circulate in the body, assisting in the fight against infection by attaching to and thereby neutralizing or destroying their target pathogen. Antibodies can take several days or weeks to develop after a person contracts an infection and may remain in a person’s blood for several weeks or more following clinical recovery. By detecting the presence of SARS-CoV2- specific antibodies within a blood specimen, antibody tests can determine if a person has had a COVID-19 infection. Antibody tests should not be used to diagnose current or active cases of COVID-19 or to infer immunity to future SARS-CoV2 infection. We can look forward to gaining fascinating and worthwhile insights from antibody testing in the future but, for now, it offers little immediate usefulness for Buncombe County residents who have not experienced laboratory-confirmed cases of COVID-19.

All diagnostic COVID-19 testing conducted at Deerfield to this point (and indeed the vast preponderance of testing performed across the nation} has been molecular/RT-PCR. Detection of genetic material within a sample provides the greatest diagnostic accuracy available, but it requires expensive technology and trained laboratory technicians, stringent protocols, and complicated equipment, all of which equate to high cost and time lost. The United States seems to be at a bit of a loss for scaling up COVID-19 molecular testing much further, leaving us to fall precariously short of our testing goals in many areas of the country. When it comes to diagnostic testing, what we, of course, desire is a test that is inexpensive, accurate, and rapid; unfortunately, laboratory science pretty well dictates that we cannot have all three concurrently. In contrast to molecular testing, antigen testing is cheap and returns results within mere minutes, but at the sacrifice of accuracy.

In collaboration with the Buncombe County Health Department, Deerfield’s Medical Director, Dr. Will Mclean, and I are working hard to conceptualize the future of COVID-19 testing at Deerfield, how best we might utilize a combination of antigen and molecular testing to balance the competing interests of cost sustainability, time efficiency, and diagnostic accuracy.

Taryn Tindall, RN, on behalf of the Deerfield Leadership Team