Are Rapid COVID-19 Test Results Reliable?
Yash and his wife Tina are very excited to take a short break after being locked at home and working for over 14 hours daily for more than a year. The run up to their leave was very hectic and as a result, they went for a rapid Covid-19 test. However, during a random check at their destination, they were found to be positive even though no one else on their journey tested positive.
Yash and Tina feel terrible – they had booked a whole lot of private activities in advance and now they will not get to enjoy any of it because they have to quarantine themselves. Two, they feel immense guilt and shame about potentially passing the virus on to anyone they may have encountered while they were already carrying the virus, confident they were safe because of their false-negative tests.
What probably happened was a false negative, something that can potentially occur in a rapid Covid 19 test. A false negative occurs when the test clears you as Covid negative when in fact you are Covid positive.
So do rapid tests lie?
They do not lie; they are simply less effective than the gold standard in Covid-19 testing which is the lab based molecular PCR test.
You can take a rapid Covid-19 19 test that may be an antigen test or else a rapid molecular test. However for these tests to be potentially more accurate:
- They must be taken within 5 days of having contracted the infection
- The virus or virus protein must be present in high quantities because the molecular test attempts to detect the Covid-19 virus’ DNA and the antigen test attempts to detect the protein on the virus’ surface.
False negative versus false positive
Additionally, according to a research study published on the Cochrane Library online the rapid antigen tests are a lot more likely to depict a false positive than they are to depict a false negative.
Antigen versus molecular rapid test accuracy
The same study also found the rapid molrcular tests to be more reliable than their antigen test counterparts.
Why have rapid test kits at all considering their low efficacy?
The same reason why there are pregnancy self tests and home use thermometers. The same reason you glance up at the sky to decide whether you need an umbrella in the rainy season. So that you can at least get a vague idea.
With Covid-19 ,testing in particular rapid test kits exist so that you have answers while you wait for confirmation.
Let’s say you live at home with your family and you start to show mild symptoms – although it could be anything. With full diligence, you visit a Covid-19 testing centre and give a blood sample. However the results might take 2 days because of the rising caseload.
At this point you are unsure of whether to isolate yourself in a part of the home, inconveniencing your family. Additionally you work in essential services. Should you go to work tomorrow? You haven’t (yet) tested positive. You’re worried you’ll get in trouble for being opportunistic and slacking off if you don’t show up and later test negative. You’re also worried about showing up and later texting positively – what if you pass it to someone and they land up being a very serious case, or worse.
In situations like this a rapid Covid-19 test can be very useful. One can even take multiple tests to be sure.
Other situations when a rapid test kit might be useful include
- When you are asymptomatic travel frequently and need to show a Covid-19 test in order to move about freely. That said you should get a lab based molecular PCR test at longer (but regular) intervals to avoid getting stuck like Yash and Tina.
- When a large number of people need to be tested.
- In emergencies.
- In situations where you need to do a test for whatever reason after vaccination.
Timing and reliability
Some studies have found – particularly for antigen tests – that they are on point 72% to 78% of the time during the first week of infection. However in the second week after having contracted Covid-19, the accuracy of the rapid antigen tests dropped to 51% or in other words, they were wrong half the time and right half the time.
Symptom presence and reliability
Interestingly, some studies have noted that in people who do not show symptoms despite being rapid antigen tests accurately delivered positive test results less than 60% of the time.
How can diligent citizens play it safe
- Do get vaccinated
- Do opt for a lab based molecular PCR test ASAP if you display symptoms
- Get a rapid test to know your status immediately
- If you have the luxury space, isolate yourself immediately
- Notify your employer of the presence of symptoms and the timeline for expected delivery of test results – a socially responsible employer should ideally let you work from home to eliminate the chance of transmission
- Opt for insurance especially if you travel frequently within the country. Yash and Tina might lose out on the money spent on their hotels and activities but if they need to be hospitalized, they have no worries because they have medical insurance that allows them to get treatment at a long list of hospitals in the country. At some hospitals, they might even be able to get a cashless hospitalization. While it’s not a happy situation, it’s better than having the financial burden of hospitalization on top of everything else.
To avoid a situation like the one Yash and Tina found themselves in, it is advisable to get a lab based molecular PCR test especially when you are travelling for leisure.