You can be covid-19 positive, even if the swab test is negative. Here’s why

We are far, far away from flattening the curve in India. If you don’t believe us, just look at the rising number of covid-19. To make matters worse, a statement by the WHO Director-General, Tedros Adhanom Ghebreyesus, has again created a wave of panic. 

He said:

But this is just the tip of the iceberg, because there’s another reason why this situation can slip out of our hands and that is: you could be positive but your covid test could be negative.

You must be thinking how on this earth is this possible? Well, let’s hear it from an expert. 

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“It is unfortunate but it is true. It has been seen in the past and we see it on a very regular basis that people are SARS-CoV-2 positive but their reports came out as negative,” says Dr Prashant Borade, head of the critical care unit at Global Hospital, Mumbai.

But how can test results of a covid-19 positive person come out as negative?
A reverse transcription-polymerase chain reaction (RT-PCR) test is the only way to identify whether the person is covid-19 positive or not.

According to media reports and an article published in the magazine Outlook, this kit isn’t all that successful because some test kits show erratic results. 

Here are the two major reasons listed by Dr Borade that lead to a false covid-19 report
Firstly we must know that if a person is tested between one to seven days after showing the symptoms of coronavirus, then there is about a 70% chance of accurate detection. But if the test is conducted after eight to 14 days, then the detection percentage falls down to 54%.

1. Sample not collected properly is also a major cause of concern
In most of the cases, it has been seen that the samples are not taken properly. Either proper scraping is not done or the swab hasn’t gone deep enough to pick up the virus.

“To collect the virus the swab needs to go deep into the pharynx. The scrapping also needs to be done in a proper manner so that the virus can be picked and it should be done for at least 20 seconds to collect the right sample,” says Dr Borade.

He also mentions that “70% covid swabs are positive but in 30% cases you may have symptoms but negative test results which is a big enough number. In case half of the people get false reports then taming this virus can be hard.”

The point is that the test is very sensitive in nature. If there is still an uncertainty then experts recommend a CT scan of lungs as it is more effective.

Dr Borade says, “The main organ hit by the covid-19 virus is lungs and with a CT scan we can detect covid-19 pneumonia with utmost ease.”

2. Patients have been on antibiotics
“It has also been seen that there are some patients who are either on steroids or on antibiotics for some prevailing illness. In such cases the immune system is already taken care of. In some cases, these patients have the symptoms of coronavirus but the swab test came out to be negative. In such cases we also do antibody tests but the fact is that it can’t replace the swab test majorly,” explains Dr Borade.

He says:

Do you know that there have been reports that even a test kit with 99% accuracy fails to detect a viral load of 50 per microlitre or less? What this means is that if there are 50 viruses per microlitre in the swab of a person, then the kit might give a negative result even if the person is infected.

Is there a solution to this?
“In case there is a lot of confusion whether the patient is positive or not we evaluate the results of swab, antibody, and CT scan test to remove the scope of ambiguity. If two out of these three are positive then we consider the patient to be covid-19 positive and treat him/her,” he concludes. 

The bottom line is that even if your covid-19 report is negative, you need to be cautious. So, keep an eye on the symptoms and consult with a doctor if you feel that your covid-19 symptoms are recurring.