Demystifying COVID-19 Testing
The Chautauqua Health
Leadership Working Group
Testing for the COVID-19 virus is a long and complex subject. This article is provided to identify most of the key points that all patients need to help understand testing as it applies to their own care.
Under normal circumstances, the U.S. FDA (Food and Drug Administration) addresses safety, appropriate use, and efficacy standards well before a test is available in the market. Due to the urgency of our current crisis, many different tests in the market that have received only “Emergency Use Authorization” from the U.S. FDA. These tests are supported by significant laboratory data but typically lack extensive clinical use.
Currently under such authorization, there are several reliable and fast COVID-19 tests available. Until recently, obtaining samples, supplies, and shipping to reference laboratories have sometimes constrained timely and convenient testing.
The good news is that COVID-19 tests are no longer being rationed as they were just a few weeks ago. Symptomatic patients in Chautauqua County can typically be tested locally with same day results (sometimes less than two hours). Additionally we can now safely meet current clinical requirements for diagnosis and public health screening, including the ’30 tests for every 1,000 residents per month’ requirement in the New York state re-opening plan.
“Do I need to be tested?” With the media attention and natural anxiety accompanying the epidemic, among the most common questions we are asked is “How do I get tested?” or “Which test should I get?” even before the question of “Do I need to be tested?”
The usefulness of a specific COVID-19 test depends on many factors. Most important is the information it can reliably provide and what you can do with that information. A test that gives you inaccurate or misleading information is worse than no test at all. If your test interpretation tells you are not infected when you are, or that you have immunity when you don’t, you are less likely to take the precautions necessary to keep yourself, family members, and coworkers safe.
Functionally, there are three types of tests:
¯ A good test is one that helps you take the correct action.
¯ A useless test may give you some information, but nothing you use for a decision.
¯ A bad test is one that guides you to the wrong action.
Technically, there are two major groups of tests:
¯ ‘Virus tests’ that detect the presence of the virus (usually in your nose or throat).
¯ ‘Antibody tests’ that detect antibodies reacting to the virus in your blood.
Tests that detect the virus: The test that is currently most available to detect the virus is ‘PCR test’ (polymerase chain reaction) which finds pieces of viral genetic material and ‘amplifies’ them by copying them over and over in a ‘chain reaction’. It is the most sensitive test available to detect an active COVID-19 infection, and the one your doctor is most likely to request.
An additional virus test that is just becoming available is the ‘antigen test’ which finds pieces of viral coat proteins. The antigen test most resembles the in-office flu tests. Though less sensitive than its PCR ‘cousin,’ it is likely to emerge as the first choice as a routine diagnostic test if it proves to be the fastest and least expensive test to administer.
Either one of these ‘virus’ tests – and only these tests – can currently detect an ‘active infection’. Consequently, they are the only tests employed to test patient with symptoms, pre-operative patients without symptoms, contacts of known or suspected COVID-infected individual in ‘virus-catching’ exercises carried out by the County Health Department, or precautionary testing of asymptomatic healthcare, senior care, emergency care and other essential workers at high risk of acquiring and spreading the infection.
Tests that detect antibodies to the virus: To fight the virus we produce antibodies once we are exposed. These can be detected by blood (serological) tests late in the course of an infection and/or thereafter. Antibody tests are an indirect way to help evaluate the clinical and public health features of COVID-19. But there are many limitations.
COVID-19 antibodies may generate some level of protection against a future infection – but how much protection remains unclear. Other more common Coronavirus infections (the common cold is one) in general do not confer lasting immunity. Case reports of reinfections and persistent positive COVID-19 tests in patients raise additional concerns about how much immunity is conferred for how long. A positive antibody test today might increase your suspicion that the nasty cough and fever you had last January was in fact a COVID-19 infection – but that doesn’t mean you have any protection from a new infection or should behave any differently to protect yourself in the next wave.
An additional complication in interpreting results is that many of the COVID-19 antibody tests ‘cross react’ with other coronavirus antibodies that may be circulating in our bloodstream from previous colds and infections. To make matters worse, COVID-19 antibody tests have a high level of ‘false positive’ results where the prevalence of the infection is low, as we see in in Chautauqua County.
Because of these limitations, current antibody tests can be ‘good, bad or useless’ depending on their application:
¯ antibody tests can be ‘good tests’ when employed in population screening applications, in particular those that are seeking to estimate infections rates and trends in large groups;
¯ antibody tests are ‘bad tests’ for determining individual infection status, and
¯ antibody tests are currently ‘useless tests’ for determining your COVID-19 immune status.
Tests in the Future: As we learn more about the virus and our immune system responses, we will make better use antibody (serological) tests to establish exposure history and potential immunity. As cheaper and faster antigen tests further develop, we may be able to search for asymptomatic carriers in schools and workplaces, enabling more effective contact tracing. While there are never any “perfect” tests, we have the tests we need to be smart about the epidemic and successfully manage individual and community health.
If you have questions about you or your family’s health, or COVID-19 in general, we’d love to try and answer them, anonymously, of course, in this recurring series. Send your questions to email@example.com or call (716) 338-0010 to leave a message.
The Chautauqua Health Network Medical Leadership Working Group includes The Chautauqua Health Network Medical Leadership Working Group includes Wolf-Dieter Krahn M.D.; Robert Berke M.D.; G. Jay Bishop M.D., FACP, FSVM, RPVI; Patrick Collins M.D.; Lynn M. Dunham M.D FAAP; William A. Geary M.D. Ph.D.; Tariq Khan, M.D., FAAP; Elizabeth (Betsy) Kidder M.D., Ph.D, MPH, FACP; John LaMancuso M.D. FACP; Tat-Sum Lee M.D., FACP, FACEP; Lillian Vitanza Ney M. D. FACP, FACC; James M. Sherry M.D., Ph.D.; and James E. Wild M.D., FAAFP.