This post will attempt to answer the following questions:
- What are the different types of tests for COVID-19?
- How are they different?
- What can they detect?
- What are potential problems with the tests?
- Can I trust the results?
- Should I take a home COVID-19 test?
Understanding the issue of testing for COVID-19 is essential to understand how COVID-19 spreads and how to stop it. In spite of this fact being clear to everyone, the implementation of wide spread testing has been difficult and painfully slow to implement. It is also nearly as difficult for people to understand its nuances. I’ll do my best to simplify the issue to help you understand.
What are the tests?
There are two basic categories of tests that need to be understood. The first is a test to determine if a person is infected. The second is a test to determine if someone has developed antibodies to the virus. This would suggest that they were previously infected and have recovered.
The diagnostic testing that has been used from the beginning is something called a PCR test. This is a technique used by biologists to amplify a predetermined piece of genetic material. For the coronavirus this test was developed by first sequencing the RNA of the virus and then creating a test to amplify that piece of RNA. This test can only tell you if the virus was in the body but not if it is active. There were many difficulties with getting this mass produced due to issues of government approval and scaling of production. You can read more about my experience with testing here. I wrote that what seems like years ago when most people had not been tested.
Another type of test that is not currently widely utilized for logistic reasons is viral cultures. This is where a sample is placed in cultures with cells and viral replication is measured. It can distinguish active from inactive virus but takes longer to get results and is more labor intensive and expensive.
The final important type of test to understand is something called and enzyme linked immunosorbent assay (ELISA for short). This test allows labs to determine the presence of antibodies specific to the SARS-CoV2 coronavirus.
Why is wide spread testing so important?
There are many reasons why testing his vital for getting us out of the pandemic. The first is the importance of identifying both who is sick and who is not sick. The importance identifying who is sick is obvious. You need to know who to isolate and who to treat. Wide spread testing would allow for identification of contagious people who have minimal or no symptoms to isolate them and prevent further spread. These individuals have been a major part of the spread of the disease because they don’t know they are infected yet are highly contagious. Identifying them would make a huge difference.
Antibody testing has a different purpose. It is essential for identifying who has recovered but can also tell you who was infected in the past and may now be immune. Because wide spread testing wasn’t implemented effectively there may be a large population that has recovered and is immune but doesn’t know it. This group could then be allowed to return to society once the details of how long immunity lasts and how effective it is are sorted out.
What are the problems with the tests?
The major problem with developing mass testing is on the production side. The techniques for developing the tests are old and easy for the laboratory testing companies to develop. The problem is getting their accuracy verified and then getting them mass produced.
It is essential that the accuracy of the tests are verified. No test in medicine is perfect. Each result comes with a probability that the result is a true result. Just because the lab report gives an answer doesn’t mean that answer is correct. Why this is important should be obvious. If someone who is actually infected gets a test result saying they are negative they could be under the false assumption that they are not contagious and then spread the disease. Alternatively, if they are not infected and get a positive result they will be isolated unnecessarily. Worse, people with a false positive result will be under the incorrect assumption that they are immune and not take appropriate precautions. If they then get infected in the future they won’t know and could spread the disease.
The exact diagnostic accuracy of the PCR for COVID-19 is not known but it is known to not be perfect. It may not even be that good. I myself have seen multiple patients who had an initial negative test with a subsequent test being positive. I even had one who was negative twice and then positive on the 3rd (in this case it was not a charm). There are many reasons why the test could be inaccurate. There could be inadequate procedures for collection, handling, transport and storage of the swabs, collection of inappropriate or inadequate material (for quality or volume), presence of interfering substances, manual errors, or sample contamination to name a few. There could be technical problems with the equipment as well.
This is why it is so important for there to be standardized testing procedures that can be regularly verified. The job of enforcement is tasked to the FDA but is a process that can take some time. Delays in FDA approval of wide spread testing were part of the reason why mass testing was so slow to take hold. Verification is vital but in a time like this there needs to be some flexibility.
Unfortunately, profit minded companies have developed rapid in-home testing. On the surface that sounds like a great idea. If people could test themselves at home this could ease many of the logistical obstacles to widespread testing. The problem is that home testing allowed without verification of accuracy will inevitably lead to more false results with all the resultant problems I mentioned above. Further, if laypeople are not trained in how to interpret the tests they may come to incorrect conclusions. There could be disastrous results if charlatan testing hits the market.
As for the antibody testing, As of the day I am writing this the FDA has not approved antibody tests for the coronavirus, but one test — made by Cellex Inc. — has been granted emergency use authorization.
Hopefully accurate, easy, mass produced, and (hopefully) cheap PCR and antibody testing will be available soon to help us get through this crisis. The important thing is that you SHOULD NOT purchase or use any testing that does not have FDA approval. The consequences could be dire for you and society as a whole. I have put forth a proposal to get us out of this crisis which will depend on accurate testing.
If you know of anyone who has wondered about the issues related to testing, please send them this post. Education will be vital to prevent people from getting scammed by home testing schemes. Please help me spread this information.