Your technique can impact your RAT test accuracy - How to know if you’re testing yourself correctly

As long as you haven’t been living in a remote cabin with no access to the daily news, there is a very good chance that you have heard of the COVID-19 coronavirus. Originally identified in 2019, this respiratory virus has dominated the public consciousness since early 2020, impacting every facet of life from mandatory lockdowns to work-from-home orders.

Declared as a global pandemic by the World Health Organization (WHO) on March 11, 2020, infection rates of COVID-19 have continued to skyrocket around the world¹. With current estimates putting the global infection total at over 386 million, it is no surprise that we have created multiple different ways to identify and diagnose COVID-19 over the past two years².

As our best defence against the spread of the disease, early diagnosis and isolation can significantly help reduce the number of potential contacts a person positive with COVID-19 may interact with. But, while this practice may sound simple on paper, logistical issues like access to tests, proper testing technique, and even the type of test you receive can dramatically impact the accuracy of your results.

So, despite the increasing importance and prevalence of COVID-19 testing, it appears that many people are still not aware of how the testing process works, and may even be at risk of doing at-home testing using less than ideal techniques. With this in mind, we wanted to share some essential information about the COVID-19 diagnostic process, while also sharing our best tips for anyone struggling with understanding the intricacies of these beneficial yet complicated tests.

The three types of COVID-19 diagnostic tests

Over the duration of this pandemic, three different types of COVID-19 tests have been developed and used as the primary way to diagnose the disease. Depending on where you live and how severe your symptoms are, the type of test you get access to can be completely different. The three different types of COVD-19 tests are³:

• Molecular-based tests (PCR, NAAT) — These styles of tests rely on analysing a person’s genetic code to detect possible changes made by the viral infection. Referred to as reverse-transcription polymerase chain reaction (RT-PCR) or DNA sequencing, this style of testing is highly sensitive, making them the best choice for detecting a COVID-19 infection as early as possible. But, because these tests require laboratory analysis, it can take extra time to get your result, especially during busy testing times.

• Antigen tests (rapid test, paper test) — Used for more immediate results, antigen testing has become the most popular form of at-home testing. This diagnostic style relies on detecting molecules found on the virus itself instead of analysing a person’s genetic code. Able to provide a result in a matter of minutes, it is important to note that the accuracy and sensitivity of these tests are significantly lower than the molecular option.

• Antibody tests (serological test, blood test) — Similar to other blood tests, this style of test relies on identifying particular immune system responses to the COVID-19 virus. Because it takes time for the immune system to recognise and react to a new infection, this test is best suited for detecting past COVID-19 infections. Additionally, antibody tests require laboratory analysis and can take multiple days to produce a result.

With this knowledge of how each test works, medical practitioners can prescribe the most accurate and beneficial test depending on your symptoms and estimated infection date.

A negative test result isn’t always accurate (depending on the test you took)

Especially when it comes to rapid antigen tests, the result you see is not always an accurate representation of the situation. Typically speaking, any COVID-19 test that is not performed by a skilled medical professional and analysed by a laboratory technician is significantly more likely to produce an inaccurate result. With one study from the Center for Disease Control and Prevention (CDC) showing that 1 out of every 5 at-home rapid antigen COVID-19 displayed a false positive, it can be hard to know if your test result is truly accurate or not⁴.

Despite this, at-home antigen testing is still incredibly important in the fight against the continued spread of COVID-19. While it is valid to question the authenticity of your at-home test, it is critical to understand that at-home antigen tests have a significantly higher chance of producing a false negative (not correctly identifying a true infection) instead of a false positive (claiming there is an infection when the person is actually COVID-19 free). Looking to better understand the difference between the accuracy of a molecular PCR test and at-home antigen testing, a recent study found that the at-home tests were still able to correctly identify 78.9% of people who had COVID-19 and 97% of those who did not⁵. So while they are less accurate than the PCR alternative, at-home tests still clearly play a strong supporting role in the fight against the global pandemic.

At-home testing is becoming more accessible

With the 2nd anniversary of the first COVID-19 shutdowns approaching in March of 2022, it is tempting to feel like we haven’t made much progress in the way of controlling and treating this viral disease. But, with at-home antigen tests now available at most American drugstores for as little as $10-40 dollars depending on where you live, we have at least increased the accessibility to testing for COVID-19 over the past two years. Additionally, free at-home COVID-19 tests are being made available in a variety of locations across the country to service those who are at high risk and may be unable to afford regular testing fees.

When you purchase one of these tests, you receive all of the needed supplies to perform the test from the comfort of your own home. Including swabs, testing solutions, and easy-to-follow instructions, the goal of increased access to at-home antigen testing is to identify and diagnose newly developing COVID-19 cases so people can isolate sooner.

How to read your at-home COVID-19 antigen test

If you are interested in taking an at-home COVID-19 antigen test, understanding how to read the results is essential for knowing what your next moves are. On most at-home tests, there are three possible results⁶:

Video: How To Interpret Self-Test Results

• A positive test result — If you receive a positive test result, it is likely that you have come into contact and have been infected by the COVID-19 virus. This result will display itself on the test strip as two prominent lines, similar to a pregnancy test positive result. If you test positive from an at-home COVID-19 antigen test, you should immediately notify your primary care provider and follow current CDC guidelines for isolation and quarantine⁷. Additionally, if you have been in close contact with any family, friends, or co-workers, they should also be notified so they can be tested to prevent additional spread.

• A negative test result — On the other hand, a negative test does not definitively rule out a possible infection. Indicated on most at-home tests as a single line on the upper portion of the test, false negatives are possible with this style of testing. If you continue to feel COVID-19 symptoms, it is advised that you test yourself again over the next few days, with at least 24 hours between tests, to get the most accurate results. If you are concerned about the validity of your test and you can book a PCR molecular test where you live, this can be done as well to produce a more definitive result.

• An invalid test result — As a sort of non-result, an invalid test result can be caused by a variety of different factors. This type of result can be shown in two different ways on the test, either as a single line on the lower portion of the test or as no lines at all. From too little testing fluid to a poor batch of tests, a wide variety of reasons can cause this result, and it indicates that the test was not able to give a result. If this happens when you perform your at-home test, retake another test if you have the option and contact the manufacturer for further instructions.

Not all at-home tests are built the same

As it turns out, even though we know that at-home tests are less effective than molecular PCR options, differences in antigen testing brands can also play a role in their efficacy. Overseen by The U.S. Food and Drug Administration (FDA), all manufacturers are required to submit clinical data about their product to determine its sensitivity (aka, how accurate it is at diagnosing a COVID-19 infection). Unfortunately, because COVID-19 tests are approved as an emergency measure, each individual brand of the test has not had time to be extensively tested to learn about its specific sensitivity and accuracy. But, while it is hard to know the specifics about which brand to choose, there is a list of approved options on the FDA website that we highly recommend you use as a baseline for selecting the type of at-home COVID-19 test you use⁸.

Your testing technique can impact its accuracy

No matter which test you take home, a major determining factor in the efficacy and accuracy comes down to the actual testing technique. With different techniques used for anterior nasal swab collections vs mid-turbinate nasal options, reading the instructions and following along with helpful videos are some of the best ways to ensure that you get the best possible specimen to be tested.

Ten tips for getting the most out of your at-home COVID-19 test

With all of this being considered, there are still a few extra pointers that can help to ensure that you get the most accurate results out of your at-home COVID-19 antigen test. Examples of tips we recommend include⁶:

• Store your test in a safe space — Keeping your tests in a safe, dry, and room-temperature environment is the best way to ensure that they are not damaged before being used.

• Double-check the expiry date — If you have an expired COVID-19 antigen test, do not use it to get a result. Additionally, if any of the components appear damaged or have a cloudy tinge, they should be thrown out.

• Use a clean surface — Before doing your test, be sure to clean off the surface you plan to use. Reducing the risk of contamination can help to lower the risk of getting an invalid result.

• Don’t pre-open your test — If you are planning on doing a COVID-19 test later in the evening, do not pre-open the package before that time. Instead, keep the package intact and in a safe place until you intend to use it.

• Read the instructions before you begin — As the best way to prevent confusion, be sure to read the instructions for your specific test before you do it. This way, you can reduce your risk of making mistakes that can lead to an invalid result.

• Watch a tutorial video — If you are struggling to understand the written instructions, watch a helpful video about using and interpreting your test instructions.

Video: How To Use A Self-Test

• Have a timer ready — Before you begin, be sure to grab a timer so you can keep track of how much time has passed after you place your specimen into the test. This can be done on a watch, stopwatch, or phone.

• Read the results in the defined timeline — It is important to follow the instructions when it comes to timing your result. Allowing too little or too much time can alter the true result, so be sure to read your test at the specified length of time to get the most accurate results.

• Don’t reuse materials — Once a test has been used, none of the components can be used again to test for COVID-19. All used tests should be disposed of to prevent confusion and potential contamination of newer tests.

• Consult with your primary care provider if you have issues — If you are having any issues with your at-home COVID-19 test and or are not sure how to interpret your results, be sure to contact your primary care provider for support. They will be able to answer your questions and provide advice about how to get the most out of your test.

Important takeaways about COVID-19 testing

While it still may feel like there are a lot of question marks floating around about the accuracy and benefits of at-home COVID-19 testing, it is important to note that they are a helpful tool in our fight against the pandemic. If you or someone you love develops symptoms of COVID-19, using an at-home antigen test is a useful and insightful way to learn more about your condition, and potentially can help to protect those around you from being exposed to the virus.

As members of the global community, it is our responsibility to follow public health measures and do everything in our power to reduce the risk of spreading the virus to others. If we are all able to work together, using these tools that we have is the best way to keep the largest number of people safe while slowing the spread of the COVID-19 pandemic.

Sources:

1. WHO declares COVID-19 a pandemic (2020)

2. Coronavirus disease (COVID-19) pandemic | World Health Organization

3. Coronavirus disease 2019 testing basics | U.S. Food and Drug Administration

4. Performance of an antigen-based test for asymptomatic and symptomatic SARS-CoV-2 testing at two university campuses — Wisconsin, September–October 2020 | Center for Disease Control and Prevention

5. Validation of an at-home direct antigen rapid test for COVID-19 (2021)

6. Self-testing | Center for Disease Control and Prevention

7. Quarantine and isolation | Center for Disease Control and Prevention

8. In vitro diagnostics EUAs - Antigen diagnostic tests for SARS-CoV-2 | U.S. Food and Drug Administration

The author, Claire Bonneau, is a medical writer and certified trauma operating room nurse.