How to understand Covid-19 RT-PCR reports?

Reverse-transcription-polymerase chain reaction is the full form of the RT-PCR test The cycle threshold value (CT value) determines whether a person is positive for Covid-19 or not. This is thought to be the accurate test that is available for this diagnosis. CT value is the number of cycles needed to amplify the viral RNA to a detectable level.

After collecting the sample RNA will be extracted and then treated with a reverse transcriptase enzyme. Then from this, complimentary DNA is extracted. Then DNA will be amplified using a polymerise chain reaction to make billions of copies of a fragment. The DNA amplification will be done in the cycle. Each cycle doubles DNA by double X2. How many such cycles are required to identify the virus is measured in this test.

According to the Indian Council of Medical Research, the positivity criteria is based on the cycle threshold (CT). This is a measure of how soon the SARS-CoV-2 is detected in a sample during the testing. If the CT value is 35 or less, the patient to whom the sample pertains is supposed to be infected with the virus. Any value higher than 35 is an indication that the patient is not infected with the virus.

RT-PCR test is done to identify the presence of the SARS-CoV-2 virus in the body of the persons sufering from Covid-19 or even if the fragments of the virusd are present in the body. It is a Reverse transcription polymerase chain reaction test and is carried on the sample taken from the mouth or nose of a person suspected for its infection. This type of polymerase chain reaction test is generally performed for detecting genetic material from an organism like virus. The test will only detect the virus if the person is infected at that time otherwise it would show negative or might show some fragments indicating that the person had suffered with it earlier.

This test is considered as the benchmark test for ascerataining the presence of infection in a person. Any person who has come in close conract of an infected person or has visited a place where high density of virus load is expected then it is necessary for him to get this test to take further preventive steps in the matter.

The PCR machine contains a thermal cycler where some chemicals are used which produce fluorescent light if they encounter the virus and by analysing this light signal a positive result is concluded if it is above a threshold value. If a person is having less number of virus in his body then it might be possible that this test may not give sufficient signal to interpret the result like that and might be concluded as negative. So in most of the cases though positive is a concluded test the negative might not be fully confirmed.

During the RT-PCR test the sample taken from the person is converted into DNA and then amplified many times for better detection of the virus. CT value is related to that amplification and based on the scientific studies it is found that if the virus is detected within a CT value of 35 then it can be taken as the positive and any value above it is indicative of absence of virus. So CT value gives a check to interpret the data more intelligently.

Sometimes the person is already cured of Covid-19 but some fragments of virus might be still in his body and that could lead to positive result but the person would not spread it and is safe himself also and it only shows that he had Covid-19 in the distant past.

It is to be noted that RT-PCR test is more reliable as compared to the quick test known as Antigen test. The Antigen test is rapid test and takes hardly 20-30 minutes to test the virus through detection of the surface proteins present on the virus. If this test is positive then there is no need of further investigation but if it does not give a correct result or negative result then one is advised to go for the RT-PCR test.

Detection of virus can be carried out through the Antigen Test and it takes less time for the detection of the corona virus. Even taking hardly 25 minutes to 30 minutes would be enough to detect the presence of surface - proteins of the virus but unfortunately this test sometimes may not be accurate providing you false results. You cannot be sure of sure of its negative result and hence it is better to go in for RT- PCR test and this test will provide you accuracy in determination of presence of SARS - COV -2 virus within the body - system. It is a polymerase chain reaction process employed for the detection of a specific organism such as the virus. This process involves the detection of the fragments of the virus even though the patient is already recovered from the corona virus.
This test is carried out by drawing samples either through the mouth or the nose in case you are suspicious of contracting this virus. However drawing through the nose is preferable for the accurate result.
This test is the surest test for diagnosis of COVID 19 because of its excellent reliability. If the result obtained is above 35, it indicates that the patient is not infected with the virus and any value less than the threshold value ( less than 35) is the indicator of the presence of infection of COVID 19.