What causes a false positive rapid COVID test?

False positives are a common occurrence in the COVID-19 world. It is because many symptoms you might experience, such as fever, nasal congestion, and cough, are similar to that caused by various other bacteria and viruses. This can be problematic if you're dealing with a serious COVID-19 infection and need to know whether your test results are accurate. Furthermore, continue reading to get detailed information on what causes a false positive rapid covid test.

Hallmarks of a rapid antigen COVID test

• Rapid antigen COVID test, also called home tests, detects the presence of antibodies formed against the coronavirus virus.
• A nasal swab is required for the test.
• Test results are available within minutes of performing the test.
• The rapid test is cheap, convenient, does not require a visit to the clinic, and can be done in any emergency.

10 Possible Causes of false positive rapid COVID test - 

A false positive is when a person without COVID-19 infection is tested positive. The rapid antigen test is designed to detect the presence of antibodies against the virus. There are several possible causes of a false positive rapid antigen test, and you may test positive for the virus in one or more of the following situations: 

1. Recently, vaccination against COVID has been given, and the immune system forms antibodies against the inactivated virus.
2. The COVID virus has recently infected you, and antibodies are still in the system.
3. Expired COVID antigen test kits: despite the test kit mentioning an expiration a year after its manufacture, the kit may have lost its efficacy within six months.
4. The nasal swab was not collected properly.
5. Presence of excess mucus in the nasal cavity while taking the nasal swab.
6. Showing symptoms of fever and cold could be another bacterial or viral infection.
7. If you have come in contact with a COVID-infected person, you may be an asymptomatic carrier of the coronavirus. Therefore, you may test positive without showing symptoms.
8. Since it is a home test kit, there can be contamination of the kit when using non-sterile techniques of performing the test, i.e., if you do not wear hand gloves or wear a nose mask while taking the nasal swab of the patient. Bacteria from your breath and hands can contaminate the test kit and provide inaccurate results.
9. Follow the package instructions and manhandle the kit.
10. Rapid test kits are sensitive to all antibodies. They are not specific to the protein on the antibodies generated specifically against the COVID virus. 

Why does a false positive occur?

False positive results are an unavoidable occurrence and can be due to the following:

Sensitivity and specificity -

THere are the two main features of a rapid antigen test. Most test kits are sensitive to detect the presence of antibodies. However, it is difficult to develop specificity of the antigen towards the specific protein present only on the antibody against the COVID infection. This specificity towards the antibody is different in various brands of test kits available in the market. And hence, if you are symptomatic with fever, cold, or congestion, you may be tested positive despite the symptoms not being caused by COVID-19.

Presence of antibodies -

Antibodies can be present in the system,

• from a recent cold or an infection
• if you were recently infected by the COVID infection but have recovered, the antibodies may still be present
• if the COVID vaccine recently vaccinated you, new antibodies are being generated 

How common is a false covid positive result?

The accuracy of the test kits depends upon the brands of the rapid antigen kits. The test kit by Coris Bio concept scored the poorest with 34% accuracy. At the same time, the test kit by SD Biosensor Standard Q scored the highest accuracy of 99%. Thus 1 in 100 people will have a false positive or negative result. According to a survey conducted for various brands, For people with COVID-19 symptoms, 67%-74% correctly tested positive, while about 30% were a false positive or a false negative. For people without COVID-19 symptoms, 58% correctly tested positive, while about 40% were a false positive or a false negative. 

How to avoid a false covid test positive?

The good news is that there are some things you can do to minimize the chances of having a false positive on a rapid COVID test. Here's how,

• While performing the rapid test at home, use nose masks and hand gloves while taking the nasal swab.
• While taking the nasal swab, take deeper, wider circles of the nasal sample to ensure a good amount of the sample.
• Blow your nose before taking the test
•  Avoid taking the test soon after being vaccinated.
• Follow the instructions mentioned in the test kit.
• Not sharing test kits or reusing swabs.

What to do after a false positive test result?

A false positive result states the presence of a virus without any signs or symptoms of the infection. If you are tested positive on the rapid antigen test and do not show symptoms, you may,

• Take the rt-PCR test to confirm the results
•  Isolate and stay home for at least 5-days after testing positive
• Wear a mask when moving around
• Sleep separately to maintain caution
• Retake the rapid antigen test after 5-days

You may end the isolation after 5 days if you test negative on the rapid test. However, if you test positive again, you may be an asymptomatic carrier of the infection, and it is best to continue the isolation until day 10 since the first testing. 

Conclusion -

Rapid antigen tests are innovative, time-saving tests that can be performed in the comfort of your home. The test results are available in a few minutes, and the accuracy rate is about 90%. Therefore, if you've been exposed to the infection or show COVID-related symptoms, it is a good idea to test yourself to keep yourself and your loved ones safe from the COVID-19 infection.