Everyone has heard the term “testing” at least a million times by now. In general, medical tests give you information about what is going on with your body and your health. During the initial phases of the coronavirus pandemic, the tests that were offered by the World Health Organization to the United States were tests that would look for the genetic component of the virus. These are the same types of tests doctors and hospitals now have to diagnose patients. Unfortunately, the lag in accurate testing resulted in a worse outbreak, leading to shelter in place orders. Currently, we are talking about returning to society but only if we can either diagnose patients and isolate them or prove someone has antibodies. Antibody tests are now talked about just as much as diagnostic tests. Let’s break down these 2 types of tests, realizing they both have limitations.
Diagnostic Test for SARS-COV2
The tests used to look for the coronavirus actually test for the genetic material of the virus. This type of test is called reverse transcriptase polymerase chain reaction, or RT-PCR. A swab collects viral particles from the back of the nose or mouth, which is where the virus replicates to cause an infection, and the lab extracts the genetic material. Because coronavirus is a RNA (ribonucleic acid) virus, a DNA (deoxyribonucleic acid) strand first has to be made. This is a complimentary copy of the RNA. That strand of DNA is then amplified using DNA polymerase. If the genetic material of the virus is discovered from the test, it is presumed positive. Testing reliability is based on the amount of disease in a population, there can always be false negatives. Furthermore, testing an asymptomatic person may not always pick up enough viral load to get a positive result.
Who needs a PCR test?
While early testing to isolate positive patients would have been helpful in February, we didn’t have the supplies or capacity to do so. Once community spread started to occur and most of the population was isolating themselves, the CDC guidelines were to only test people who were symptomatic AND who were exposed to the virus or who had recently traveled. This was due to limited testing supply. As of 4/20/20, testing has been tiered by priority. You can see in the link that all 3 top priority levels involve symptomatic patients. The message remains that for mildly symptomatic patients who do not need hospitalization, to stay at home and isolate with rest and fluids. Although asymptomatic people may be the link to spreading and controlling the spread of coronavirus, testing capacity will need to increase before everyone can get a test.
Antibody test for SARS-COV2
Antibody tests, known as serology testing, are used to see if someone has been exposed to, or infected with, a bacteria or virus. Antibodies are proteins called immunoglobulins made by the immune system to attack foreign invaders. Each antibody is a specific match to another protein called an antigen, which lives on the surface of bacteria and viruses. Testing for antibodies does not always diagnose an active infection. While one type of immunoglobulin, IgM, is elevated during an active infection, it is not a good diagnostic tool. The test that everyone is currently interested in is the IgG test. This is the immunoglobulin that forms during the course of infection but is often not present until afterward. The timeline of IgM production and presence in the bloodstream versus IgG production and presence in the bloodstream, varies from infection to infection. IgG is considered a memory immunoglobulin so these tests are often used to look for immunity to infection. However, it is unclear if having IgG to SARS-COV2 infers lifelong immunity. At the time of publication, FDA approved testing for antibodies is still emerging, although some tests have received emergency use approval.
Who should get an antibody test?
Anyone who had symptoms of coronavirus beginning at least 14 days prior to testing would be eligible for an antibody test. The question remains, what to do with the results? Someone who had previously known or suspected COVID-19 can get an antibody test to tell them if they would be eligible for plasma donations to sick patients. The idea is that these antibodies could help fight the infection. For people who work with a high risk population, like in a nursing home or in healthcare, a positive antibody test might guide decision making on when to return to work. For people in a high risk group, it’s unclear if having antibodies means you are no longer at risk.
Anyone who receives an antibody test would need to review the results with their doctor. People with positive results or someone who had symptoms but has a negative antibody test may still need a PCR test to confirm infection. Only time will tell if a positive antibody test infers long lasting immunity.