With the number of positive COVID-19 cases rising exponentially across the globe, testing for the virus has ramped up. The need to determine just how many positive cases there are is a contributing factor in slowing the spread, helping those who require serious medical attention, and developing vaccines and treatment.
Due to the severe nature of the virus and its highly contagious attributes, testing everyone who has the virus, whether they exhibit symptoms or not, has never been more important. There are currently a few different testing options for COVID-19, so what are the benefits of a serology test over a PCR test for SARS-CoV-2 coronavirus?
What is a PCR test?
The most widely used test for COVID-19 has been the PCR test (polymerase chain reaction). The test works by singling out the genetic material of the virus in the blood to help confirm whether or not it is present in any given patient. At the time of writing, PCR tests are in short supply due to the sheer number of people needing to be tested, thus a strain on the medical community and supplies of PCR tests is occurring across the globe.
Although the PCR test is an effective way to determine a positive result in someone with COVID-19, it can be expensive and takes time to process. Considering time is of the essence when it comes to the current pandemic, the PCR test may not be the most useful. The test also comes with its own set of downfalls. Its efficacy relies heavily on its proximity to when the patient was first infected, and in the days following, the likelihood of false negatives can rise to as much as 50%.
Why is serology testing necessary?
A serology test is done in the later stages of COVID-19 infection, and detects antibodies in the patient’s system that are developed naturally to help fight the infection on a cellular level. The serology test can be more effective than the PCR test because the window of time in which the test can be performed is greater; serology tests are usually performed 5–10 days following infection, whereas PCR tests can produce a false negative by that time. The timeline for testing acute cases is shorter, and a PCR test should be the first round in a series of different methods designed to confirm infection.
When it comes to confirming cases, a PCR test is generally better in the short-term. When it comes to tracking data of cases and community spread of the virus, however, a serology test is necessary. The serology method is especially helpful in detecting antibodies in those who were never tested due to lack of symptoms. As some cases (roughly 20-50%, according to recent studies out of China and Iceland) don’t present with any symptoms, it’s important to conduct serology testing to get a real picture of how many people have been infected with the virus but fought it off without falling ill.
How accurate is a SARS-CoV-2 serology test?
BCA’s SARS-CoV-2 serology test looks for the presence of IgA antibodies. This is due to the fact that IgA antibodies (as opposed to IgM antibodies) tend to have higher affinity rates with coronaviruses and respiratory illnesses in general, thus producing more accurate results in testing. The serology test tracks the S1 domain of the spike protein of the virus to help single out these IgAs. The accuracy of the serology test for COVID-19 sits at around 85–95%.
In simpler terms, antibodies are the proteins created by the body to help fight off infection cells. They are created by the immune system as a sort of warrior team and attack the virus at the source. When the serology test is conducted, it searches for the presence of these fighter proteins, which leads to confirmation that the infection was in fact present in the body at one point or another. The S1 domain of the spike protein is the most specific to SARS-CoV-2, so by tracking it, we greatly reduce the risk of false positives.
How can you track asymptomatic people with coronavirus?
It’s incredibly difficult to track those with COVID-19 if they have not been tested. This is especially true because those who do not exhibit symptoms are much less likely to be tested in the first place, because they don’t immediately require testing (nor are they aware they need it). This inability to track the true number of cases makes gathering data on the community transmission of the virus much harder. It can also hinder treatment and vaccine creation.
Testing members of the public who may have had the virus but did not exhibit symptoms (or those who have already recovered from the virus) could also lead to possible treatment for the sick or a prophylactic for essential workers. By using donations of hyperimmune plasma containing the antibodies used to fight off the virus, patients will receive a set of antibody ‘warriors’ equipped with the knowledge of how to fight COVID-19.
Can a PCR test detect a virus in an asymptomatic patient?
As mentioned above, the accuracy of a PCR test depends solely on the length of time between the test and the initial infection. Although it can determine whether or not the virus’ genetic material is in a person without symptoms, it’s a lot less likely that someone who doesn’t exhibit symptoms will get tested in time to heed a positive result.
Any further devastation caused by the spread of this strain of coronavirus will depend highly on testing, self-isolation and social distancing measures put in place, and the rate at which data and antibody collection can be performed.