DNA Explainer: RT-PCR or Rapid Antigen test? Which test is better

According to Health Ministry data released on Tuesday morning, India has recorded only 19,556 new coronavirus infections in the past 24 hours, the lowest since early July. The country's total number is now at 1,00,75,116. The number of Covid-related deaths reported from across the country in this period was 301, taking the total to 1,46,111.

Maharashtra, Karnataka, Andhra Pradesh, Tamil Nadu, and Kerala remained the worst-hit states, though others like Delhi, West Bengal, and Madhya Pradesh also reported high number of fresh cases in the past 24 hours.

Today we discuss the difference between the RT-PCR test and the Rapid antigen test available in the market to detect Covid-19. Broadly there are two types of tests available in the market to do a Covid-19 detection - the RT-PCR (Reverse transcription-polymerase chain reaction) test and the Rapid Antigen test. All the tests available in the market for testing of COVID-19 have their own pros and cons but RT-PCR remains the gold standard for testing. 

Advantages of RT-PCR test

The RT-PCR (Reverse transcription-polymerase chain reaction) tests, detects the presence of viral Ribonucleic acid (RNA). It is very accurate and efficient. This test is able to detect a COVID-19 infection even before the person becomes infectious and will allow early isolation. Thus, this method is able to prevent the transmission of the virus to other hosts.

As per experts, RT-PCR test has a specificity rate (ability to identify those without the disease) of nearly 100%, whereas the sensitivity rate (ability to identify those with the disease) of about 67%. This means, RT-PCR test will not give false positives but there are 30-35% chances of getting false negatives. 

Disadvantages of RT-PCR test

The disadvantages are the financial cost compared to the antigen tests, the longer evaluation time, and the need for highly professional staff for sample handling. 

At the initial stage of the Coronavirus pandemic, RT-PCR test was priced at Rs 4,500 but now the cost has been brought down to Rs 2,500. It is still expensive and takes a day to give results.

Advantages of Rapid Antigen test

The Rapid Antigen test, detects viral proteins. The rapid antigen test reveals patients at the peak of the infection when the body has the highest concentration of these proteins. Rapid Antigen Tests (RAT) has helped in a substantial increase in testing in the country and especially in the national capital Delhi. 

Their advantage is the price, the result within 30 minutes and lower demands on the expertise of the staff. 

Disadvantages of Rapid Antigen test

However, it’s a known fact that RAT can give a high number of false negatives. A few months back, the Delhi High Court pulled up the Delhi's AAP government for choosing Rapid Antigen Testing (RAT), as the primary test of COVID-19 infection over RT-PCR (Reverse transcription-polymerase chain reaction) which is considered as the gold standard for testing.

The disadvantage is that they are not as sensitive (accurate) as the standard RT-PCR tests used to accurately identify those infected. When using them, a significant percentage of those infected pass the test as a false negative. In a few days, these people will spread the virus among others, thinking they are healthy.

If you are being tested with the Rapid Antigen test, you are NOT guaranteed to be uninfected at the time of taking the test.

According to the ICMR protocol, if RAT gives negative result and an individual has symptoms of influenza like illness, then he/she should undergo RT-PCR test.