COVID-19 Testing: What You Need To Know

As I learn more about COVID-19 and share that information with you, my community, I’m increasingly asked about testing. Time is moving on and it’s clear that one of the limitations regarding the management of this global pandemic has been testing, or more specifically the lack of testing. There are still so many questions about how widespread SARS-CoV-2 (the virus that causes COVID-19 disease) is here in Alberta, Canada, and across the globe. We know that many people carry and spread the virus without showing any symptoms or just display very mild ones, but how many people are we talking about? 

As we enter the next phase of pandemic management, as people begin to enter communities again, testing will play a key role.1 It’s incredibly important to know who’s been exposed as well as who hasn’t and therefore may still be at risk. More widespread testing will help to keep those most vulnerable, including those with pre-existing conditions safe. 

While there’s undoubtedly still a lot to learn, in this article I’ll distill for you what I know and believe, as of now. I’ll cover:

  • Some background on testing, including understanding the timeline of COVID-19 infections
  • Types of testing, including viral RNA and antibody 
  • What test results mean
  • Test accuracy
  • Next steps for testing

Background on testing: The viral timeline 

To understand testing it’s helpful to understand the timeline of COVID-19 infection. This image was compiled by the Institute for Functional Medicine and provides a helpful visual.2 It’s important to note that this timeline is based on the data that has been collected so far, and some of it hasn’t been peer-reviewed and published yet. 

As you can see, the first thing that can be detected after exposure and with the onset of symptoms is the virus itself. This is depicted by the red and purple lines in the graph. 

After the initial infection, the body begins to mount an immune response and develop antibodies. This is depicted by the orange, blue, and green lines. 

Most of the testing that’s been done so far, mainly in hospitals, has been conducted when people are symptomatic. It’s also important to note that the time between when someone’s exposed to the virus and when they begin showing symptoms is widely variable. Some will show symptoms two days later and others may not show symptoms for three weeks. Others will show no symptoms at all, or only mild ones, yet still be spreading the virus during the first couple weeks of infection.

Time Course for testing after Exposure to SARS-CoV-2
Source:  https://p.widencdn.net/n3trkt/IFM_Sars_Graph_v3

Types of testing

There are two main types of testing, namely viral and antibody. Both have their place in the timeline of events. 

The Viral RNA tests look for an active viral infection. They test for the presence of RNA (ribonucleic acid) from SARS-CoV-2. The test will be positive for someone with a current or very recent infection.3 This test can be undertaken using several methods of collection.

  • Nasopharyngeal swab – This goes into the nose about three or four inches. 
  • Oropharyngeal swab – This down the throat and is similar to a test for strep throat. 
  • Sputum – This is the thick mucus produced by the lungs during an infection. If this can be collected from a person’s coughing, it can be tested. 
  • Saliva – Saliva collection for this test works best after a cough.
  • Stool – Viral RNA can be detected in the stool after an infection.4

A positive test result doesn’t necessarily mean that you’re contagious and are ‘shedding’ the virus. In order to verify that, we’d need to culture your sample in a laboratory. However, there are issues with safety and containing the virus in a laboratory setting, so this type of testing is mostly only done in a research environment at the moment. 

Therefore, we’ll assume that a positive test means you’re contagious and that you need to quarantine for two weeks in order to protect others. It also means that you should watch for symptoms and seek medical care if needed. You can read about treatment options, including herbs and nutrients, here. Tracking positive testing is also important from a public health perspective, in order to trace the spread of the virus.  

Viral RNA testing is going to be most accurate around four to six days after symptoms appear, since this is the peak of the viral RNA production.4 If you wait too long to be tested, you might get a negative Viral RNA test, even though you were infected. This is why this testing has a high false negative rate. You need to get the timing right. If you have a negative test, but a known exposure, you’ll still need to take precautions and may need to be tested again. 

The second type of test that’s helpful is an antibody test. This is a blood test that studies your immune response to the viral exposure. Essentially, it’s looking to determine if you were exposed to SARS-CoV-2 in the past and may be particularly helpful for mild or asymptomatic cases.5 The best time to take the test is about seven days after symptoms resolve or a minimum of fifteen to twenty-one days after exposure. 

There are two main antibodies that current testing is looking at.

  • IgM – This non-specific antibody is produced as the immune system is figuring out exactly what it’s dealing with. If you look at the chart above, you’ll see that IgM rises and then fades away as more specific antibodies (IgG) are produced. 
  • IgG – This more specific antibody takes a little time to develop and then stays high for a period of time.6

This pattern that we’re seeing with SARS-CoV-2 antibodies is typical of what we see with other viruses. 

A positive test suggests that you’ve been infected and that your body mounted an immune response to the infection, whether you had severe symptoms, mild ones, or no symptoms at all. Timing matters here as well. If you test IgG antibodies too early, you might miss them because they take some time, possibly around three weeks, to develop. False positive tests are also possible as some of the tests are detecting previous exposures to other coronaviruses, such as the ones that cause the common cold.4

A negative test might mean that you still need to take precautions to prevent exposure, especially if you’re at higher risk for severe COVID-19. Because of the timeline, it’s important to note that a negative antibody test does not rule out current infection. 

As you can see, the testing is quite nuanced, which is why connecting with your healthcare team for guidance is so important. 

Understanding test accuracy

Naturally, we want a test to be accurate, to be both sensitive and specific. This will limit false positive and false negative results. 

When it comes to accuracy, sensitivity refers to how likely a test is to pick up a positive result in those that have definitely been infected, known as true positives. It’s those that have been exposed to the virus that test positive. Specificity refers to individuals that haven’t been infected by the virus that test negative, which are referred to as true negatives.7. In a perfect world we always want a test to be 100 percent sensitive and 100 percent specific, but this isn’t the case when it comes to coronavirus testing. It can also be similar for many other antibody tests. The poor test results for Lyme disease detection are a good example of this.

We’ve already seen that there are cases of false positives and negatives based on timing and other factors. For example, with a viral RNA test, the nose swab can be really unpleasant so it’s possible that an error can occur as a result of not going deep enough to collect the appropriate sample. Alternatively, there might be low sensitivity because the test picks up antibodies to another coronavirus that are connected to a previous coronavirus infection.4

You might also hear the terms positive predictive value (PPV) and negative predictive value (NPV) in discussion regarding test accuracy. These take into account sensitivity and specificity in terms of the infection rates in a specific population.7 Of course, we need more testing to determine what rates are in each area. This article in Scientific American provides a useful guideline to the testing.

If I have the antibodies, am I immune? 

A conservative answer to this question is that we don’t know for sure. Because this virus is new, we don’t know if everyone that’s exposed develops antibodies, if those antibodies truly mean immunity, and if so for how long.4

However, it’s likely that this virus acts like other viruses that we know more about. For example, for a coronavirus that causes a common cold, you get the cold, develop antibodies, and those antibodies protect you for a while. For something more severe than a cold, such as chicken pox, you can develop immunity for a lifetime. 

You may have heard stories of those that tested positive, negative, and then tested positive again sometime later. However, this is more likely to be an issue with testing methods and timing more than a case of the immune system not creating immunity.  

That being said, I do think that having positive antibodies will be a tool that’s used to help open society up and allow individuals to return to daily life with more confidence.  

Should I get tested?

While I do think that widespread testing is important for both the individual and society, the availability of testing is still quite limited. 

There are many laboratories working to address the issues of access. These include functional testing laboratories, that are frequently used by myself and my colleagues, which are now coming to the market with tests. I have some colleagues that prefer one test over another and others that are waiting for the testing to become more accurate before widely applying it to their patient population. Another factor is that testing through private laboratories is quite expensive. At some point the cost will come down and testing will become more widely available. 

In Canada, we only have access to the provincial laboratory services, whereby they’ll perform PCR testing and antibody testing provided the correct criteria are met. If a private test is requested, we’re able to use certain US-based laboratories. Diagnostic Solutions Laboratory ships their COVID test kits to Canada. They have three test options, which are nasal swab, antibody and stool. 

A German laboratory called Euroimmun AG introduced a test with 100 percent specificity, thus eliminating the chance of a false positive. It’s been approved in the USA. A full list of all the tests approved for diagnostic purposes in all countries is included here at the Center for Health Security website. The Mayo Clinic has also launched an antibody assay with a specificity of 99.3 percent when tested against normal serum. Approximately three percent of serum is IgG positive less than seven days post-symptom onset, 35 percent are IgG positive in samples collected between eight and fourteen days after symptom onset, and 100 percent are IgG positive after fourteen days of symptom onset.

We’ve learned a lot so far about SARS-CoV-2 and COVID-19, but still have plenty that we need to understand. I’ll be keeping a pulse on the new research as it becomes available and will continue these important discussions with my colleagues in order to keep you updated regarding the very latest information. My understanding of this virus is that it’s evolving day by day and although testing is relatively new, it’s still extremely important. 

As we navigate this next wave of outbreak management, testing will be key in order to understand who has active infections, who’s already been exposed, and who may still be at risk. Testing will help us to understand how the virus is spreading, answer important questions about immunity, and ultimately to save lives. My sense is that until the antibody testing can approach a specificity that’s close to 100 percent, it may be worthwhile to wait it out.  

Please don’t hesitate to reach out for support as needed. My team and I are always here for you during this challenging time. 

References: 

  1. Patel R, Babady E, Theel ES, et al. Report from the American Society for Microbiology COVID-19 International Summit, 23 March 2020: Value of Diagnostic Testing for SARS-CoV-2/COVID-19. mBio. 2020;11(2):e00722-20. Published 2020 Mar 26. Full text: https://mbio.asm.org/content/11/2/e00722-20 
  2. The Institute for Functional Medicine. The Functional Medicine Approach to COVID-19: Primer on SARS-CoV-2 Testing. https://www.ifm.org/news-insights/functional-medicine-approach-covid-19-primer-sars-cov-2-testing/ 
  3. Wölfel R, Corman VM, Guggemos W, et al. Virological assessment of hospitalized patients with COVID-2019 [published online ahead of print, 2020 Apr 1]. Nature. 2020;10.1038/s41586-020-2196-x. Abstract: https://pubmed.ncbi.nlm.nih.gov/32235945
  4. The Institute for Functional Medicine. The Functional Medicine Approach to COVID-19: Primer on SARS-CoV-2 Testing Webinar. Hosted by Dr. Patrick Hanaway with Dr. Helen Messier. April 28, 2020. 
  5. Guo L, Ren L, Yang S, et al. Profiling Early Humoral Response to Diagnose Novel Coronavirus Disease (COVID-19) [published online ahead of print, 2020 Mar 21]. Clin Infect Dis. 2020;ciaa310. Full text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7184472/ 
  6. He-wei Jiang, Yang Li, Hai-nan Zhang, Wei Wang, Dong Men, Xiao Yang, Huan Qi, Jie Zhou, Sheng-ce Tao. Global profiling of SARS-CoV-2 specific IgG/ IgM responses of convalescents using a proteome microarray. Preprint article: https://www.medrxiv.org/content/10.1101/2020.03.20.20039495v1 
  7. Abdul Ghaaliq Lalkhen, MB ChB FRCA, Anthony McCluskey, BSc MB ChB FRCA, Clinical tests: sensitivity and specificity, Continuing Education in Anaesthesia Critical Care & Pain, Volume 8, Issue 6, December 2008, Pages 221–223, Full text: https://academic.oup.com/bjaed/article/8/6/221/406440 

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