Delhi Capital's Mitchell Marsh tested COVID+ in an antigen test but negative in RT PCR testing; Know all about the difference between the two and why it may have happened

Australian all-rounder Mitchell Marsh has been admitted to the hospital after he tested positive for COVID-19 in his second RT-PCR test. The Delhi Capital player had tested negative in his first mandatory RT-PCR test, which was conducted after he tested COVID positive in a Rapid Antigen Test (RAT). The officials confirmed that the Australian cricketer showed some symptoms and therefore had to undergo a test.

"A few more members from the Delhi Capitals bio-bubble, including support staff members, have returned positive tests as well. Though they are all asymptomatic, their condition is being monitored closely by the franchise," Delhi Capitals said in a statement.

Also read: Coronavirus: Canadian study finds COVID-19 deaths higher during weekends than weekdays; here's why

"All remaining members of the bubble are currently in isolation in their respective rooms, and will be tested regularly," they added.

Many like Marsh have had such experiences where they tested positive in an antigen test, but landed up with a negative RT-PCR test. Let us find out in detail what it means.

Image credit: IPL

There are many ways to get yourself tested for COVID-19. However, an RT-PCR and an antigen test are the most popular among them all.

RT PCR is considered the most accurate form of COVID testing. The swabs taken from a person's throat or nose or both are sent to the laboratory, where scientists look for the RNA, or the genetic component of the virus. The presence or absence of the genetic material reveals whether a person is positive or negative for COVID-19, respectively.

But unlike an RT-PCR, a rapid antigen takes less time to deliver results. This is because an RT-PCR looks into the entire virus RNA, while an antigen test uses the technology that traces only the protein in the virus strain. That said, while a molecular test can take up to a day to showcase results, a rapid antigen test can give results within 10 to 30 minutes.

There could be several factors that determine the accuracy of the tests and why you can get a negative result with an RT PCR test even if you have classic COVID-19 symptoms such as a fever, a sore throat, fatigue, body pain, cough and more.

While many experts have attributed it to the test's purported inability to detect new coronavirus variants, others believe it could be due to the low viral load in the body. Post-infection, the symptoms of COVID-19 typically appear 2–14 days after exposure and the virus begins to manifest by the fifth day of an infection cycle. That said, if a person gets tested any sooner, he or she is likely to get a false negative.

Additionally, a false positive or a false negative result also depends on how efficiently the swab stick was inserted into your nose or throat. In case the samples were not collected appropriately, it may lead to a false negative/positive result.

Some of the classic COVID symptoms include:

- Fever

- Persistent cough

- Sore throat

- Fatigue

- Muscle and joint pain

- Loss of sense of smell and taste

- Runny nose

- Sneezing

- Gastrointestinal problems

You can also get antibody tests or serology tests to determine your COVID-19 status. However, it is a type of blood test that helps detect whether you have had COVID-19 in the past. An antibody test does not detect an active coronavirus infection, rather detects the presence of the viral particle, several days post-infection. Therefore, this type of test is only recommended 14 days after symptoms onset.

Currently, at-home COVID-19 Antigen Self-Test has gained a lot of popularity. This type of test requires no medical assistance. It is like a rapid antigen test that delivers results in no time. However, similar to an antigen test, there are chances of false negative/positive results, which is why experts recommend taking an RT PCR test, if you have come in close contact with a confirmed COVID-19 case or experience coronavirus-specific symptoms.