Last Updated on April 9, 2020 by Sagar Aryal
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So far we have discussed three tests currently authorized by the Food and Drug Administration (FDA) for the diagnosis of COVID-19. All the discussed techniques are molecular-based tests that aim at detecting the presence of the SARS-CoV-2 genome (RNA).
For the diagnostic tests, there are two objectives to their working principle.
- Molecular-based test that aims at detecting the presence of SARS-CoV-2 RNA
- Serological tests aiming at qualitatively detecting the antibodies/immunoglobulins the host produces to the virus, anti-COVID-19 immunoglobulins or detecting the viral antigen in the host.
Definition of COVID-19 IgG/IgM Rapid Test
The COVID-19 IgG/IgM is a Rapid Diagnostic Test that detects the body’s immune response to the virus. This test is effective because it can detect the body’s response in the asymptomatic phase, during the infection and even after recovery from COVID-19.
So, why IgG and IgM antibodies? Because IgM is the first specific antibody that is produced by the body in response to infection followed by IgG, which replaces the IgM as the predominant antibody as the infection progresses.
IgM and IgG fight infection by targeting specific antigens on the surface of the SARS-CoV-2, and therefore, immunoglobulin tests are used to detect viral antigens to detect IgM and/or IgG antibodies against those antigens.
The test has a 91% clinical specificity rate and a 99% clinical sensitivity rate and uses antibodies in blood to identify current or past coronavirus infection.
Objectives of COVID-19 IgG/IgM Rapid Test
To detect for the presence or absence of IgM and IgG anti-COVID-19 antibodies in patients showing symptoms of COVID-19.
Principle of COVID-19 IgG/IgM Rapid Test
The COVID-19 IgG/IgM Rapid Test detects IgM and IgG antibodies in a rapid test that gives results within 2 to 10 minutes. The test which is user friendly has the COVID-19 IgG/IgM Rapid Test Device (capillary kit), which is a qualitative membrane-based immunoassay for the detection of COVID-19 antibodies in whole blood, serum, or plasma.
The kits are designed differently by each producing company and we will look at the producing companies at the end of this discussion. But however the design, the working principle is the same. The test aims at detecting for the presence of IgG and/or IgM antibodies produced during COVID-19 infection. If the individual is in the asymptomatic phase of at least 3-7 days of infection, the kit should be able to detect for IgM antibody, which is the first antibody produced early into an infection. And if the individual is in the symptomatic phase, what is known as the secondary stage of infection, the IgM and IgG antibodies can both be detected. This is because, as the infection persists, the immune system also produces the IgG antibody as the second antibody as it also continues to produce IgM antibody. And if the Individual is recovering or has recovered from the COVID-19 infection, the test will indicate the presence of IgG antibody, which still remains in the system until the infection is completely eliminated. But if an individual has no infection, only the control line will appear on the test kit.
The kit is designed in that it uses a capillary lateral flow chromatographic Immunoassay. It is also small and portable and can be used at Point of Care (POC).
Procedure for COVID-19 IgG/IgM Rapid Test
- Collect 2-3 drops of fresh blood/serum or plasma from a finger prick or venous blood and place it in a sample well and place 2-3 drops of provided buffer in the same sample well.
- This allows the diluted sample to move through the capillary tube by capillary action
- The capillary kit has labeled SARS-CoV-2 antigen that may bind chemically with either IgM or IgG; thus, forming an antigen/antibody complexes of antigen/IgG and/or antigen/IgM.
- After that reaction, the antigen/antibody product passes over anti-IgM and anti-IgG antibodies that are immobilized in a line within the capillary kit.
- The anti-IgM and/or anti-IgG then will capture the specific complex and signal a result (a red line) if either complex is bound to the immobile anti-IgM or anti-IgG.
- The results need to be read after 10 minutes and no more than 15 minutes.
Results and Interpretation
Three detection lines are possible, the control with (C) line appearing when the sample has finished flowing through the cassette, indicating the test is complete, the positive and negative lines.
- Negative Result: If only the quality control line (C) appears and the detection lines IgG and IgM are not visible, then no COVID-19 antibody has been detected and the result is negative.
- Positive Result, IgM only: If both the quality control line (C) and the detection line IgM appear, then the COVID-19 IgM antibody has been detected and the result is positive for the IgM antibody.
- Positive Result, IgG only: If both the quality control line (C) and the detection line IgG appear, then the COVID-19 IgG antibody has been detected and the result is positive for the IgG antibody.
- Positive Result, IgG and IgM: If the quality control line (C) and both detection lines IgG and IgM appear, then the COVID-19 IgG and IgM antibodies have been detected and the result is positive for both the IgG and IgM antibodies.
- Invalid results when there is no control line.
Immunoglobulin tests for COVID-19 can only confirm if you have been exposed to the virus (Presently or in the past) depending on the antibodies detected by the test and not to confirm the presence of the virus in your system. Consequently, it should only be used alone as a screening test and should be used in tandem with a genetic-based test to determine a complete status. Genetic testing is the gold standard for COVID-19 diagnosis.
- They are fast (rapid) producing results within 10 minutes
- They are small and portable hence can be used at Point-of-Care (POC)
- Some of the test kits have a 90-95% sensitivity and specificity factor.
- They can only be used for screening and not as the gold standard test for COVID-19.
- Some of the test kits have low sensitivity and specificity.
Companies that have designed COVID-19 IgG/IgM Rapid Test Kits
Several companies have designed the COVID-19 IgM/IgG Rapid Diagnostic tests and here are a list of some of them.
- Cellex Inc. qSARS-CoV-2 IgG/IgM Rapid Test (FDA authorized)
- Bodysphere (http://www.mybodysphere.com/sars2covid19.html)
- Confirm Biosciences (https://www.confirmbiosciences.com/coronavirus-test/)
- RayBiotech (https://www.raybiotech.com/covid-19-igm-igg-rapid-test-kit/)
- Novus Biologicals Bio-Techne Brand (https://www.novusbio.com/products/covid-19-igg-igm-rapid-test-kit_nbp2-89106)
- Dynamiker Biotechnology (Tianjin) Co., Ltd. (http://en.dynamiker.com/index/index/pro_info/aid/606.html)
- Confirm Biosciences COVID-19 IgG/IgM Rapid Test Cassette
- FDA Bodysphere’s Two Minute COVID-19 test for Emergency Use
- 19% – https://www.medicinenet.com/how_do_the_covid-19_coronavirus_tests_work/article.htm
- 2% – https://www.truecare.org.uk/
- 2% – https://www.biomedomics.com/products/infectious-disease/covid-19-rt/
- 2% – https://www.amdiagnostics.com.au/covid
- 1% – https://www.medicalplasticsnews.com/mpn-north-america/rapid-diagnostic-test-for-covid-19-rolled-out-in-the-us/
- 1% – https://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/UCM533023.pdf
- 1% – https://www.abbexa.com/coronavirus-covid-19-test
- <1% – https://www.sciencedirect.com/topics/immunology-and-microbiology/immunoglobulin-m
- <1% – https://www.researchgate.net/publication/23164645_Lateral_Flow_immunoAssay_Its_Strengths_Weaknesses_Opportunities_and_Threats_A_Literature_Survey
- <1% – https://www.nature.com/articles/s41368-020-0075-9
- <1% – https://www.nature.com/articles/d41587-020-00010-2
- <1% – https://www.justanswer.com/medical/33xb6-positive-hsv2-igg-antibodies-level-5.html
- <1% – https://www.cliawaived.com/amfile/file/download/file/1263/product/6506/
- <1% – https://irp-cdn.multiscreensite.com/2e086463/files/uploaded/HBP%20Trust%20Screening%20Covid-19%20Test%20Device.pdf
- <1% – http://english.tjbh.com/system/2018/01/12/030316545.shtml