SARS-CoV-2 IgG Antibody Testing 

Antibody testing could be a vital tool for determining who has already been infected and might have immunity to the coronavirus . Serology testing for SARS-CoV-2 is at increased demand in order to better quantify the number of cases of COVID-19, including individuals that may be asymptomatic or have recovered. 

 

Many individuals may benefit from serology testing as nearly 81% of infected people are asymptomatic or have mild to moderate symptoms.

Cogent utilizes the Access SARS-CoV-2 IgG assay, which has been validated against 1,400 negative broad population-based samples—significantly more than the number of samples required by the FDA for Emergency Use Authorization › The Access SARS-CoV-2 IgG has 100% sensitivity and 99.8% specificity—one of the highest combined rates for SARS-CoV-2 antibody tests in the market.

Get High Medical Value with Targeted Antibody Identification

To identify an immune response against the SARS-CoV-2 coronavirus, it is important to target the right antibodies.

  • The Access SARS-CoV-2 IgG assay is designed to target antibodies against the coronavirus spike protein that may be more likely to confer immunity.

  • Laboratory studies show that to identify an immune response against the SARS-CoV-2 coronavirus, it is important to target the right antibodies

  • The Access SARS-CoV-2 IgG assay detects antibodies to the RBD (Receptor Binding Domain) of the spike protein, which may be important for immunity, based on laboratory studies

  • In addition, studies show that antibodies against the RBD are neutralizing, which may indicate that these proteins are an effective measure of immunity when compared to antibodies against other SARS-CoV-2 viral proteins

What does IgM and IgG mean for Covid-19 testing?

Understanding what antibodies do for us is key in interpreting your lab results. Generally, IgM is the first antibody developed against an antigen and is detectable from 4 to 7 days. IgG is developed 7 to 14 days after the infection and can be detectable for months and years, depending upon the antigen and the individual. 

Immunoglobulin M (IgM) IgM is produced in our bodies in the first 4 to 7 days when a Virus is present.  IgM is the largest antibody, and it is the first antibody to appear in the response to initial exposure to an antigen.

Immunoglobulin G (IgG) IgG is the antibody that is produced 7 to 14 days after a virus is present, and takes over as the "long term" antibody that continues to fight off the virus. This antibody represents approximately 75% of serum antibodies in humans, IgG is the most common type of antibody found in blood circulation. IgG molecules are created and released by plasma B cells. Each IgG has two antigen binding sites.

Interpreting Antibody Lab Results

     IgM      IgG                     Result Interpretation

    NEG(-)             NEG(-)          - No exposure to the virus, or could be consistent with very early active infection prior to IgM production

    POS(+)             NEG(-)          - Acute infection present; IgM develops within a few days of exposure in most individuals

    POS(+)             POS(+)         - There is a short window period (approx. 2 weeks into infections) where both IgM and IgG are detectable

          NEG(-)             POS(+)         - Pattern expected in those who have  successfully cleared the virus and now may have a degree of immunity

Medical Value of Targeting the Spike Protein

Though the coronavirus uses many different proteins to replicate and invade cells, the spike protein is the major surface protein that it uses to bind to a receptor. After the spike protein binds to the human cell receptor, the viral membrane fuses with the human cell membrane, allowing the genome of the virus to enter human cells and begin infection. 

The coronavirus spike protein mediates entry into host cells by attaching to a receptor on respiratory cells called angiotensin-converting enzyme 2, or ACE2. Antibodies against it may promote neutralization of SARS-CoV-2. 

A coronavirus contains four structural proteins, including spike (S), envelope (E), membrane (M) and nucleocapsid (N) proteins.

Source: J Peiris, Y Guan & K Yuen, Sever acute respiratory syndrome, Nature Medicine Supplement 2004, 10 (12)

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