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Updated on April 23, 2020

RT-PCR test (reverse-transcription polymerase chain reaction test) is an established test for detecting viral infections as well as some tumours. It was also one of the first successful diagnostic tests used for the detection of the new coronavirus - SARS-CoV-2 - which causes COVID-19. In fact, doctors started using this test to diagnose COVID-19 infection as early as January 2020 - just weeks after the world found out about this new coronavirus infection.

The Indian Council of Medical Research (ICMR) has approved the use of this test for COVID-19. Read on to know more about this test:

  1. What is an RT-PCR test?
  2. Why is an RT-PCR performed?
  3. How do you prepare for an RT-PCR test?
  4. How is an RT-PCR performed?
  5. What do the results of RT-PCR test mean?
  6. Doctors for COVID-19 Test

RT-PCR or reverse transcriptase-polymerase chain reaction is a diagnostic test that is used to look for the presence of nucleic acids, specifically RNA (ribonucleic acid), in a given sample. 

Nucleic acids are long-chain polymers of sugar, phosphate and a nitrogenous base. They include both DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

In a human body, DNA is responsible for coding all the traits - ranging from your eye colour to the colour of your hair and the number of toes you have. RNA, on the other hand, is a messenger, that carries the message (code) of the DNA so the cellular machinery can translate it and make proteins. In a human cell, DNA stays in its place inside the nucleus - a small organ inside the cell.

However, some viruses do not have DNA. Instead, their RNA serves as their genetic material. Common RNA viruses include the hepatitis C virus, influenza virus and coronaviruses like SARS virus, MERS virus and the SARS-CoV-2 virus that causes COVID-19.

Polymerase chain reaction or PCR is a technique that is used to makes clones or several (millions of) copies of DNA or RNA or specific sections of a DNA or RNA chain. To make the copies of DNA, the PCR machine uses the enzyme DNA polymerase, which is responsible for cloning DNA in body cells every time a cell divides. 

An RT-PCR is a specific kind of PCR that can amplify RNA. It is occasionally used in clinical settings to look for viral RNA. RT-PCR is a much more effective method than looking directly for the presence of viral antigen (specific proteins released by the virus against which the body produces an immune response) since even a small amount of RNA can be used to diagnose the condition.

Most RT-PCRs give results in real-time - real-time reverse transcriptase PCR.

Read more: How are COVID-19 samples collected?

Your doctor may ask you to get an RT-PCR test done for the following reasons:

  • To detect the presence of certain viruses, for example, the influenza virus, and SARS-CoV-2.  
  • To look for the presence of certain types of cancer and tumour RNA circulating in your bloodstream.
  • To detect the presence of certain genetic diseases. Since RNA codes for protein production in cells, RT-PCR can be used to study the expression of genes in the body.

Read more: What is the cost of testing for COVID-19?

No special preparations are needed for an RT-PCR test. Your doctor will tell you if you need to fast before the test. 

Tell your doctor if you are taking any medicines, herbs or supplements as these may affect the results of this test.

Read more: Who needs to get tested for COVID-19 infection?

For an RT-PCR, a sample can be obtained from your blood (for circulating tumour RNA, for example). A nasopharyngeal (nose) or oropharyngeal (mouth) swab is taken to collect samples for COVID-19 diagnosis. If you are a suspected COVID-19 patient, the doctor will be in full PPE while taking the swab. A swab is a long flexible rod usually made of plastic (though it may also be a steel rod) and having a tip made of rayon, polyester or flocked rayon. 

The blood sample for this test will be obtained from a vein in your arm. 

A nasopharyngeal swab is taken in the following way: 

  • You will first be asked to blow your nose into a tissue. This will remove all the extra mucus from your nose and help them take the swab easily. 
  • Next, your doctor or a lab technician will ask you to tilt your head back to 70 degrees.
  • He/she will then put a swab stick through your nostrils and take it to the back of your nose, making sure that it steadily moves through the base of your nose.
  • The swab will be allowed to stay in this position for a few seconds so it can absorb any and all secretions.
  • After this, the technician/doctor will slowly pull the swab out while gently rotating it.
  • The swab will be put in a sterile vial and sent to a lab for analysis.

For an oropharyngeal swab, the swabs are collected from the back of your mouth in a similar way.

If you are getting tested for COVID-19, the technician will likely to take a nasopharyngeal or oropharyngeal swab sample.

Normal results:

Normal results for the RT-PCR mean that there was no viral RNA or no RNA of a tumour was found in the given sample. Or the gene expression is normal - in case the test is done to look for a genetic condition.

Abnormal results:

Abnormal results for an RT-PCR indicate that the RNA of the virus or the tumour was found in the given sample or faulty gene expression was noted.

RT-PCR also indicates the viral load in the body - the amount of viruses present in the body. This is very important since viral load is used to differentiate between active and persistent (chronic) infection in the body.

Depending on the results of this test, your doctor will determine the treatment.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.

Dr. Neha Gupta

Dr. Neha Gupta

संक्रामक रोग

Dr. Lalit Shishara

Dr. Lalit Shishara

संक्रामक रोग

Dr. Alok Mishra

Dr. Alok Mishra

संक्रामक रोग

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References

  1. Rio DC. Reverse transcription-polymerase chain reaction. Cold Spring Harb Protoc. 2014;2014(11):1207–1216. Published 2014 Nov 3. PMID: 25368309.
  2. Centers for Disease Control and Prevention [internet]. Atlanta (GA): US Department of Health and Human Services; Information on Rapid Molecular Assays, RT-PCR, and other Molecular Assays for Diagnosis of Influenza Virus Infection
  3. Yamaguchi Kazuya, et al. Significant Detection of Circulating Cancer Cells in the Blood by Reverse Transcriptase–Polymerase Chain Reaction During Colorectal Cancer Resection. Ann Surg. 2000 Jul; 232(1): 58–65. PMID: 10862196.
  4. Diamantina Institute: The University of Queensland [Internet]. Australia; Polymerase Chain Reaction (PCR)
  5. Etienne Lucie, et al. Single Real-Time Reverse Transcription-PCR Assay for Detection and Quantification of Genetically Diverse HIV-1, SIVcpz, and SIVgor Strains. J Clin Microbiol. 2013 Mar; 51(3): 787–798. PMID: 23254130.
  6. Science Direct (Elsevier) [Internet]; Reverse Transcription Polymerase Chain Reaction
  7. Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002. From DNA to RNA
  8. Victor Corman, Tobias Bleicker, Sebastian Brünink, Christian Drosten. Diagnostic detection of 2019-nCoV by real-time RT-PCR. German Center for Infection Research (DZIF) at Charité – Universitätsmedizin Berlin, 17 January 2020.
  9. Notification by Ministry of Health and Family Welfare, Government of India [Internet]. ICMR guidelines for COVID-19 testing in private laboratories in India.
  10. Marty Francisco M., Chen Kaiwen, Verrill Kelly A. How to Obtain a Nasopharyngeal Swab Specimen. The New England Journal of Medicine. 2020 April.
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