Description:
COVID-19 RDT qualitatively detects IgG and IgM antibodies to SARS-CoV-2 in human whole blood, serum or plasma samples. This test applies lateral flow immuno-chromatography and is a tool to assist in the diagnosis of SARS-CoV-2 infections. It is also intended as a tool for carrying out serological epidemiological investigations. This test kit is for healthcare professional use only.
What are IgG and IgM?
IgG and IgM are immunoglobulins, also knows as antibodies themselves, are important components of our immune system. When we get an infection, such as COVID-19, these immunoglobulins are produced, which attach to the virus and activate the rest of the immune system to attack and clear the virus. IgM is the first immunoglobulin to be produced and is a general antibody that can bind to many different types of pathogen. The presence of IgM is an indicator of early infection. IgG is a more specialized antibody that specifically binds to the SARS-CoV-2 virus. The presence of IgG is an indicator of later stage infection (usually 7 days or longer after infection).
Test Attributes:
- Whole blood, serum, or plasma may be used for testing
- Results available in only 10 minutes
- Easy to use
- Results can be read visually
- No need for an analyzer
- Cost effective method for assisting in diagnosing COVID-19 disease.
Materials:
Contents:
a test cartridge,
- a vial of sample dilution buffer, and
- a brochure insert with information about test principle, procedure, and interpretations.
Procedure:
- Bring the the test cartridge and buffer solution to come to room temperature.
- Transfer 10 μl of the sample to the center of the sample well with a dropper supplied or a micropipette with tip if not.
- Allow the sample to absorb into the well and then transfer 3 drops of the buffer into the well.
- Read the results after 15 to 20 minutes.
Principle:
The COVID-19 RDT is a qualitative lateral flow immunoassay for the simultaneous detection of IgM and IgG antibodies to SARS-CoV-2 in whole blood, serum or plasma specimens.
The test cassette contains recombinant SARS-CoV-2 antigen conjugated to coloured particles.
When a specimen is added to the sample well of the cassette, any IgM and IgG present in the specimen will bind to the antigen conjugate, forming coloured coronavirus antigen-antibody complexes.
This mixture migrates laterally along the membrane to the test region. In this test region, anti-human IgM and anti-human IgG have been immobilised onto the membrane. These capture any IgM and IgG complexes that have formed, resulting in the appearance of coloured lines.
Therefore, if the specimen contains SARS-CoV-2 IgM antibodies, a coloured line will appear in the IgM test line region. If the specimen contains SARS-CoV-2 IgG antibodies, a coloured line will appear in the IgG test line region. To serve as an internal control, a coloured line will always appear in the control line region, indicating that the proper volume of specimen and buffer has been added, and correct procedure has been followed.
Interpretations:
The present IgM/IgG serological assay is designed to complement RT-qPCR in the diagnosis of SARS-CoV-2 infections. Table 1 shows the clinical interpretation of all possible scenarios that can be encountered when testing a patient with both RT-qPCR and an IgM/IgG serological test.
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| Table 1: Clinical Significance of IgM/IgG RDT Results |
The table is based on the current knowledge about the rise and fall of SARS-CoV-2 RNA and antigens, IgM antibody and IgG antibody (Figure 1) and the correlation of these level variations with the initial time of infection, onset of symptoms and recovery phase. As shown in Figure 1, serological tests are recommended to be used on patients at least 3 days after onset of symptoms or 7-10 days after infection with the virus.
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| Figure 1: Variation of the Levels of SARS-CoV-2 RNA and Antigen, IgM and IgG after infection. |
The key takeaway is that the results of RT-qPCR and IgM/IgG serological tests do not necessarily need to agree. A disagreement between the two tests, if any, can often be traced to the after-infection time points at which the tests were performed. Overall, while RT-qPCR testing may be appropriate for the detection of the SARS-CoV-2 virus during the acute phase, IgM/IgG is an appropriate test during the chronic phase. Since the exact time of infection is often unknown, combining RT-qPCR and IgM/IgG testing can improve the accuracy of the COVID-19 diagnosis.
Source: diazyme, biopanda, sugentech, icmr
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