Testing methods of CORONA – ANTIGEN, ANTI-BODY all tests explained.

There is a lot of confusion about various TESTING METHODS of CORONA available in the market currently.
So, let us see various types of CORONA TESTS along with some advantages and disadvantages about each.

Basically there are 2 TESTING METHODS OF CORONA

  • Antigen testing 
    • detection of a protein present on the virus
  • Anti body testing 
    • detection of immunity cells of body against the virus

Various sites are used for collection of sample to detect  COVID-19 antigen-
These are collected by inserting a ear bud like structure deep into the nose or mouth.
upper respiratory sample sites include-
1. nasopharyngeal sample (97%)
2. mid trubinate (100 %)
3. nasal swab (95%)
4. saliva (85%)
Testing methods of CORONA - ANTIGEN, ANTI-BODY all tests explained.
nasopharyngeal swab collection
lower respiratory sample sites –
1. sputum
2. BAL (broncho-alveolar lavage)
3. Tracheal sample
Testing methods of CORONA - ANTIGEN, ANTI-BODY all tests explained.
oral swab collection

Generally 2 swabs – nasopharyngeal swab and oral swab are taken for RT-PCR testing
AND
1 swab – nasopharyngeal swab is taken for RAPID ANTIGEN TESTING.
Let us see what are the various antigen testing methods of CORONA along with their advantages and disdvantages.
Testing methods of CORONA - ANTIGEN, ANTI-BODY all tests explained.

1. RT-PCR (Reverse Transcriptase Polymerase Chain Reaction)

Gold standard for covid antigen detection. This is the best test for detecting corona antigen.
the targets of these test are the Rd Rp gene(RNA dependant RNA polymerase) and 2 structural gene E (envelope) and N (nucleocapsid) and ORF 1 ab gene (open reading frame 1a and 1b)
 

  • Advantage
    • Can run upto 90 samples in single batch
    • high sensitivity
    • Disadvantage
      • Takes 4-5 hours for single batch

      2. TrueNat and CBNAAT 

      it is a small chip based neuclic acid amplification test.
      it used small chip based protable battery operated device.
      it detects the genetic operated device.

      • Advantage
        • take 30-60 minutes for single batch
        • present in wide areas and at grass root levels such as district and primary health centres
        • Disadvantage
          • 1-4 samples in single batch.

        In India, All COIVD-19 tests conducted through RT-PCR, TrueNat and CBNAAT are reported to ICMR.

        3. RAPID ANTIGEN TESTING TEST

        Recently, Rapid testing kits aka RAPID POINT-OF-CONTACT (PoC) antigen detection test have been introduced for faster on-field testing of corona antigen.

        NAME OF KIT- Standard Q COVID-19 Ag kit
        This is a rapid chromatography immunoassay for qualitative detection of specific antigens to SARS-COV-2.
        This kit has been developed by SD Biosensor company with manufacturing unit at Manesar, Gurugram
        This test must be conducted within 1 hour of sample collection in extraction buffer.
        • ADVANTAGES 
          • does not require special machine or skills
          • can be interpreted with naked eye.
          • interpreted within 15-30 minutes
          • high specificity – 99.3% – 100%
          • only nasopharyngeal swabs
        • DISADVANTAGES
          • low sensitivity – 50.6% – 84% (higher viral load correlated with higher sensitivity)
        These Rapid anitgen testing kits have high false negative results, meaning if your results for this test turns out negative, you can’t be sure if this result is reliable or not.

        According to the guidelines laid out by ICMR, all symptomatic but negative(according to rapid test kit) patients should undergo real time RT-PCR.

        HENCE-

        • those who test negative by rapid antigen test should be definitely tested sequentially by RT-PCR.

        • Positive test should be considered as true positive and does not need reconfirmation by RT-PCR.

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        FELUDA (FNACS 59 editor limited uniform detection assay)
        It is a paper based Covid test kit developed by CSIR (council of scientific and industrial research) and IGIB (institute of genomic and integrative biology), delhi. this has been approved by DCGI (drug controlled general of india).
        this used CRISPR (clustered regularly interspaced short plindromic repeats) CAS 9 technology.
        the reading of these rests are quite easy. the paper are visual readouts on a strip of paper. the cost of each paper strip is 500 indian rupees. the sensitivity is 96% and the specificity is 98%. the time taken for each test strip to show result is approximately 45 minutes.
        this testing kit has been commersially launched n indian market by TATA medical and diagnostic limited as TataMD CHECK CRISPR test.

        COVID-19 ANTIBODY DETECTION TESTS-

        Antibodies are developed in a person’s blood after he got infected by the virus. It usually takes around 14 days for the body to form IgG anti bodies against a particular virus or bacteria. Hence antibody testing is not for detecting acute infection and act as a suppplementary tool for corona testing. 
        These should be carried out atleast 14 days after onset of synptoms These are carried out to survey the presence of anti body in a population/ healthcare officials. ICMR has set out specific guidelines as to in whom such testing should be done. 

        Blood samples are taken from a person’s body for detection of anti bodies. There are 2 methods of detecting if a person has corona anti bodies or not.

        ANTIBODY TITRATION TEST – 
        These are carried out in specific laboratories. The benefit of this testing is that it also shows amount of covid anti bodies present in the body and hence can be used to measure the trend of rise or fall of anti body levels in the body.
        these tests detect the level of Ig G, IgM and Ig A antibody levels in the body.

        METHODS – ELISA (enzyme linked immunobased assay) and CLIA (chemiluminescence immunoasssay) assays. 
        ICMR has validated only ELISA kits for COVID-19.

        COVID KAVACH ELISA
        this is a unique testing kit developed by ICMR (indian council of medical research) and NIV (ational institute of virology), Pune for testing of covid antibodies.
        this is an ELISA based testing kit. 
        the sensivity of this is 98.7% and specificity is 100%. it detects the presence of Ig G anti body in the blood sample. 
        the best part about it is that the sample taking and conducting requires minimal biosafety and biosecurity as compared to RT-PCR. 
        Disdvantage – the disadvatage of thei test is that it only detects the IgG anitbodies in th body. these IGG antiboies show in the blood only after more than 2 weeks from the infection. hence this is not usefull in detecting whetehr the perso is currently sufferign from COVID 19.
        Hence, these kit s are used in sero-surveillance of population.
          

        CORONA IS NOT DETECTED BY ANY BLOOD SAMPLE.
        IT IS THE ANTI BODIES THAT ARE DETECTED BY BLOOD SAMPLES.

        BLOOD TESTS FOR CORONA

        Actually speaking, there are no blood tests for corona

        There are a few blood tests that help us determine how severe is the patient’s condition.
        These tests can also be used to determine the disease progress and progression of CORONA.
        In some cases, these can even collectively point towards the probability of having CORONA.

        So these are ‘indirect ways’ of detecting corona.

        These tests incude-

        Some countries have started deploying DOGS on airports to detect CORONA virus. Do you think that’s reliable method of checking ???
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        SOURCES-
        1. ICMR advisory on newer additional stratergies for covid-19 testing.
        2. ICMR advisory on use of Rapid Antigen Detection test for COVID-19
        3. www.emedinexus.com/post/18051/ 
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