What is the difference between RT-PCR and Rapid Antigen Test?

In this age of travel restrictions at airports and other entry points to a state or a country, coronavirus tests have become a part and parcel of our lives. The two most common types of tests are the RT-PCR and the Rapiden Antigen Test. Let us understand the difference between the two

The RT-PCR test stands for Reverse Transcription–Polymerase Chain Reaction Test. It is considered the gold standard for diagnosing viral diseases like COVID-19 and Ebola. It is a lab test that amplifies a tiny amount of genetic material, that is RNA, from a pathogen such as a virus.

It is a highly specific test meaning that if someone is infected with the virus, there is a very high likelihood that the result would come back positive. However, this means there is still a small chance that the test may show a positive result for those who do not have the infection. This is known as a false positive. RT-PCR could also detect residual virus even after the individual is no longer infected.

The first step in the test is to collect a sample of secretions from the back of the nose using a long swab with a soft end. Chemicals are then used to extract the genetic material from the sample which in this case is the RNA. The sample contains a mix of both the person’s and the virus’ RNA if infected. 

Using an enzyme called the reverse transcriptase, which stands for RT, this RNA extracted from the sample is then converted into DNA. Since the virus that causes COVID is a single-stranded RNA-based virus, the genetic material has to be converted to double-stranded DNA for the purpose of amplification.

Miniscule portions of the DNA go through 35 to 40 times of amplification so that billions of copies of viral genetic material are created. With the help of fluorescent dye, a sample is identified to be positive or negative based on the brightness of the fluorescence using a specialised equipment. This entire process can take up to 8 hours.

While on the other hand, the Rapid Antigen Test for COVID-19 can provide result within 15 minutes. This is a lateral flow test much like a pregnancy test. It can be done at a clinic, hospital or even at home. This test detects the presence of proteins on the surface of the coronavirus called antigens.
 
Since the test is not as sensitive as RT-PCR, it tends to be more accurate when used in the first few days of the onset of symptoms when the largest amount of virus is present in the body.

While it is significantly cheaper compared to RT-PCR, the major downside is that it may not always be accurate. They are the preferred method when it comes to mass testing a population.  If an antigen test is negative, RT-PCR test is recommended to confirm the same.

Among the two tests, the RT-PCR is considered to be more reliable worldwide. It is not as quick as the antigen test, but is far more accurate and time-tested.

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