The scale and accuracy of the testing for the SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) virus , the cause of COVID 19 is in a gradual state of evolution in India, with new and improved kits being developed by biotech companies worldwide.
The three widely used methods include – Antibody Testing (IgG), Reverse Transcription Polymerase Chain Reaction (RT – PCR) method and TrueNat. They are all different from each other. They have their strengths and limitations, advantages, and disadvantages.
Real-time RT-PCR continues to be the most trusted and accurate process till date. However, no individual process is 100% accurate due to the changing characteristics of the virus.
Antibody test (IgG)
Antibody testing is also known as serological testing. Your doctor or medical laboratory technician will use it to examine the type of antibodies present in your blood. Your antibodies are protein molecules. They bind to the foreign particles like viruses (in this case) and alert your immune system to take action against it.
There are numerous antibodies in the blood. The technician or nurse will collect a sample of your blood and examine it for IgM and IgG. Ig stands for an immunoglobulin molecule.
● IgM antibodies develop at an early stage of infection against SARS-CoV-2.
● IgG antibodies develop against SARS-CoV-2 once the person has recovered from coronavirus.
Enzyme-Linked Immunosorbent Assay (ELISA) is a type of antibody test. It is designed to screen a wide area in a short period.
Results by Antibody Test (IgG)
The antibody testing kits take around 30-60 minutes to show results.
Advantages of Antibody Test (IgG)
● Antibody testing is useful to screen a large number of specimens in a short time.
● They are helpful to calculate the rate of infection as of how rapidly is the virus spreading.
● It is useful to conduct surveys to enquire whether the population is exposed to the virus or not.
● It is also used to assess the factors affecting the severity of the infection.
Disadvantages of Antibody Test (IgG)
● These tests have a high margin of error. The antibody kits can provide you with the result within 30-60 minutes but are not more accurate than nasal-swab tests.
● Tests for detecting the presence of IgM antibodies can deliver results within 20 minutes. On the other hand, tests for detecting the presence of IgG antibodies can take up to a week. IgG tests are more reliable than IgM.
● Faulty results – there arises a question of assurance of the quality of tests. The tests do not provide or guarantee 100% accuracy. Few kits perform better than another.
● There is an increased inaccuracy in testing asymptomatic patients.
RT-PCR comes under the category of rapid tests widely used by various countries.
Reverse Transcription Polymerase Chain Reaction (RT – PCR)
A polymerase chain reaction test is a highly sensitive test. Due to its increased sensitivity and high fidelity, it is known as the most accurate testing method for COVID 19 to date. It works by detecting the presence of genetic material from a specific pathogen. RT–PCR was widely used during the times of the Ebola virus and the Zika virus.
The trained professionals will collect a swab from your nose or throat. It will be treated with several chemicals that are capable of removing protein and fats to extract only the RNA present in it. This RNA is made to go under reverse transcription to form a viral DNA. A real-time RT-PCR undergoes 35 cycles with the viral DNA and produces around 35 billion copies. It contains sections of viral DNA. The sections of DNA emit a fluorescent dye if the virus is present in it.
Results by RT-PCR
RT-PCR is capable of delivering an accurate diagnosis and result for COVID 19 within 3 hours. The laboratories take 6-8 hours to derive a conclusive result.
Advantages of RT-PCR
● RT–PCR is highly specific and sensitive to the virus.
● Its accuracy and precision level is higher than other methods.
● It is less prone to contamination which limits the margin of error.
● It can detect the severity of the infection.
Disadvantages of RT-PCR
● It is capable of detecting only the ongoing infection. This limitation restricts doctors from understanding the development and spread of the virus. This creates uncertainty.
● RT-PCR testing needs specific instruments. It is not so simple to operate like the antibody testing, which only requires a kit.
● Using portable RT-PCR machines requires specialized training to prevent any misuse of the same.
● It is expensive.
TrueNat is a chip-based, portable RT-PCR machine that was initially developed to diagnose tuberculosis. You can confirm your sample using confirmatory tests for SARS-CoV-2 if you test positive by TrueNat Beta CoV.
Results by TrueNat
It is capable of producing faster results than standard RT-PCR tests.
Advantages of TrueNat
● It is PCR-based testing and is reliable.
● High primer sensitivity and specificity
● Contamination/evaporation resistant design
● It enables same-day testing and reporting. This allows for faster patient isolation if required.
Disadvantages of TrueNat
There are no significant limitations reported for TrueNat. TrueNat is based on PCR technology and will have the same disadvantages as RT-PCR testing.
Testing capacity continues to be a tough challenge for all. Rapid antibody tests are speed effective but cannot detect an asymptomatic patient. An asymptomatic patient will not show any symptoms but is capable of infecting you. For this in-depth detection of SARS-CoV-2, testing like RT-PCR and TrueNat are highly accurate. This was a detailed look at different types of approved tests that are being carried out for COVID-19 detection.
Most of the countries around the world have turned to PCR-based testing because they are dependable and the fastest to develop as antibody testing is generally a cheap, faster and easily-scalable alternative in certain settings.
Huge variations in testing methods and quantities from country-to-country make the numbers between countries incomparable in any actual sense. But nationwide, standardized procedures and tools for widespread testing are being adopted.