COVID-19: Why some people are testing negative despite having symptoms?

Amid the tumultuous second wave of the coronavirus pandemic, there are many cases that exhibit symptoms of COVID-19 but the lab test returns a false ‘negative’ or a false ‘positive’ in case of a person from coronavirus infection.

Why some people are testing 'negative' despite having COVID symptoms or why are some testing 'positive' despite no infection?

COVID-19 Testing in India

The two approved methods of testing COVID-19 in India are RT-PCR testing and Rapid Antigen Testing (RAT). A ‘positive’ report confirms the presence of COVID-19 infection.

However, if a person gets a negative result by RAT testing kit but exhibits symptoms of the infection, he or she is still treated whereas a negative report by RT-PCR test is confirmatory of the absence of COVID-19.

The positive or negative outcome also depends a lot on the process of sample collection, transport, and testing method.

 COVID-19 Sample Testing

The process of sample collection for COVID-19 testing is done through two processes: RT-PCR (Real-Time Reverse Transcription Polymerase Chain Reaction) and RAT (Rapid Antigen Testing).

RT-PCR is a more reliable and confirmatory way of testing COVID-19 while RAT is used more for screening purposes.

Medical practitioners or staff insert a swab into the nostrils and throat to collect tissue samples which are then placed in a liquid chemical that makes sure the virus remains active. The samples are stored in an adequate and safe setting to be transported to the path lab with bio-safety level-2.

The whole sample collection process is carried out in accordance with the guidelines mentioned by the World Health Organization (WHO).

Then why do tests return false ‘negative’?

Most of the time, the RT-PCR method returns accurate test results. If a person is infected with COVID-19, it will show ‘positive’ and ‘negative’ in case of no infection.

However, in some cases, a false ‘negative’ has been noted, which means the person has COVID-19 and he or she is exhibiting symptoms, but the result came ‘negative’.

The most likely reasons for tests to return false ‘negative’ are:

•The person was not swabbed correctly, meaning the swab test was not done accurately.

•The quality or quantity of the sample collected was not sufficient to return accurate results.

•The liquid chemical used to store the swab sample was not adequate to keep the virus active.

•The transportation or storage during the transportation of the sample was not up to mark.

•The duration from the time of collection and testing at the lab was not done in a timely manner.

•The staff conducting the test at the labs are not trained enough, hence a chance for errors.

•Health experts also note that incidentally, the RT-PCR test for COVID-19 has a sensitivity of only around 66 per cent. That means most likely one-third of infected people will return a false ‘negative’.

•Experts also speculate that if an infected person has a low viral load at the time of sample collection, most likely the result will be a false ‘negative’.

•Also, the mutant variants are also known to be notorious to go undetected in lab tests.

What if the test returns a false ‘positive’?

There have been cases where people with no infection have tested positive for COVID-19. Such is the case for people who have recovered from COVID-19 and got tested later.

Health experts say that even when the virus dies and becomes inactive, it still stays in the system for several weeks. Hence, in such cases, the lab test is most likely to return a false ‘positive’.

Advice by health experts on COVID-19 test results

In case of a false ‘negative’ or false ‘positive’ COVID-19 test result, experts advise immediately to get in touch with the concerned doctor.

Do not take the test results as a confirmatory result in case you are exhibiting symptoms.