How Accurate Are At-Home COVID Tests?
Spring is here and in the US it feels like the end of COVID-19 is here, too. People are conducting themselves in a mostly normal fashion since the pandemic began in early 2020. The advance of vaccines, natural immunity, testing and individual responsibility have had major impact on defeating the virus. But, coronaviruses do not magically go away, they stay around for years, maybe forever. There are many parts of the world where COVID is still a huge problem, and that can easily find its way to the US. Take a look at cities in China, and other places around the world.
What you’re seeing now in the US is people who have a sense they may have exposed themselves to the virus, or have symptoms, doing a test to make sure they are not going out and spreading the virus. The government has made free at-home tests available and you can buy them from sources locally and online. Everyone should have at-home tests conveniently available.
The question is: How reliable are the results?
It is important to understand testing in general to answer this question accurately. Testing for the presence of any disease or problem requires it to be present to detect it. That may sound confusing, but take this example. You know when your car is not working right and you know something is wrong so you take it to the shop. But, when you get there, the problem has gone away, or isn’t a big enough problem to figure out what’s causing it. That can be frustrating.
Another example. You’re sick. You make a doctor’s appointment for a week later. But, by the time the appointment comes up you already feel better.
At-home testing is very accurate, IF the virus is substantially present in enough quantity or ‘load’ for the test to detect it. Positive test results are virtually 100% reliable. Negative tests are said to be not as accurate, maybe 80-90%. Why? The simple answer is that the virus is not present enough for it to be detected. It doesn’t really mean the test isn’t accurate, what it means is that you do not have enough of the virus present to detect it. In fact, you may not have any coronavirus at all. You may have a little, or even more, but not enough for the at-home test to detect it.
When you send your sample away for a PCR test, it is important to understand that this test is much more sensitive, and will yield a higher percentage of positive tests. That makes sense but it does not mean the at-home tests are less accurate, it means they are less sensitive. It is also worth noting that testing for tiny amounts of the virus may not have a significant impact on controlling it, or how you feel.
You may have one patient that reports they are sick with all the COVID symptoms. The at-home COVID test was negative, and the PCR test was also negative. This confirms they were sick with something besides COVID. Another patient tests negative on the at-home test. But, this patient doesn’t have any symptoms. The PCR test is positive. What this means is that there was not enough virus present for the at-home test to detect it, provided, of course, they did the at-home test properly.
If you feel like you have come in contact with someone who is positive for the virus, or if you have symptoms, you should wait a day or two, and do a home test. If you are negative, you can go the extra mile and get a PCR test. This is arguably the best way to limit the spread of the virus.
From the outset fighting the virus has relied on learning and being responsible about spreading the virus. It may seem COVID is over but don’t totally let your guard down. Continue to be vigilant. Use the at-home tests and PCR tests so you don’t spread the virus to a vulnerable person.