Antibody Test for Covid-19

ANTIBODIES & ANTIBODY TESTING IN COVID-19

Antibody response to infections

Antibodies are proteins produced by the human body in response to an infection and help fight it off. They can stay in the blood for months to years and help in countering future attacks by the same infection.

There are 2 main types of antibodies IgM and IgG. As a rule of thumb, in most infections, IgM arrives on the scene first (usually within a week to 10 days) and at least a week later, IgG appears. However, this pattern varies from disease to disease. IgM then slowly peters out while IgG persists for years and can provide future immunity against the causative microorganism.

So, usually detection of IgM indicates that the infection is still in its acute phase and detection of IgG indicates the infection has passed.

Immune response to COVID -19

So far, scientific data suggests that, in COVID-19, antibodies can appear anytime between 5 days to 3 weeks after the onset of symptoms.

In many other viral infections, the quantum and the virulence of the virus in the patients decline by the time antibodies appear. However, in COVID-19, viral shedding is detectable for a few days even after antibodies are seen. Also, unlike other infectious diseases, detection of IgM does not indicate an acute infection and IgG, a past infection. This is because of the variable time of appearance of IgM and IgG in relation to each other in SARS CoV-2 - IgG can appear later, at the same time or earlier than IgM.

Because of this, detection of total antibodies, rather than the subtypes (specifically IgM or IgG) has more significance in a clinical context.

It has also been shown that almost 95-99% COVID-19 positive patients produce varying quantities of antibodies as they recover. Some might take a longer time to produce the antibody.

Whether these antibodies confer an acquired immunity to the patient against future infection is unclear at this moment, although one would like to believe so.

Diagnosis

RT-PCR has been the mainstay in the diagnosis of the disease from the beginning. This is a direct diagnostic test and a positive result is confirmatory of the presence of COVID-19 infection. A positive antibody test, on the other hand, is only a surrogate marker of a recent infection. Therefore, ANTIBODY TEST, BY ITSELF CANNOT BE USED FOR DIAGNOSIS OF AN ACTIVE INFECTION.

When used judiciously and in combination, the results of RT-PCR and antibody tests can be of great help in stratification of the population vis-à-vis actively infected population, recently infected but recovered population, and the normal population.

An algorithm based on these considerations is given below as a general guide for the population at large (source: CDC, Atlanta, USA). The reader is encouraged to follow these guidelines and help the healthcare and regulatory authorities in controlling and, if possible, in eradicating this pandemic.

TestResultInterpretation
Viral testing (Testing for current infection – PCR/Antigen)PositiveMost likely have an active infection
NegativeMost likely do not have an active infection
Antibody testing (Testing for evidence of past infection)PositiveLikely had a COVID-19 infection in the past
NegativeLikely never had a COVID-19 infection or never developed antibodies to a past COVID-19 infection
BothViral Positive, Antibody PositiveMost likely have an active infection
Viral Positive, Antibody NegativeMost likely have an active infection
Viral Negative, Antibody PositiveLikely had and recovered from a COVID-19 infection
Viral Negative, Antibody NegativeLikely never had a COVID-19 infection

Antibody Test For COVID-19 FAQ

  • What is an antibody?

  • Why would a person want to have a COVID-19 antibody test performed?

  • What does the COVID-19 antibody test do?

  • Can this test be used to diagnose COVID-19 infection?

  • Does this test correlate with the severity of the disease?

  • How are antibody tests performed?

  • How long does it take to receive test results?

  • Who all are eligible to be tested?

  • If I presently don’t have COVID-19 symptoms, should I get the test?

  • If I have a positive COVID-19 antibody test, am I protected against future infections?

  • Are there any other benefits to doing this test?

  • When can this test be done?

  • Is social distancing needed if I have antibodies?

  • How much does the COVID-19 antibody test cost?

  • Are there health concerns to taking the COVID-19 antibody test?

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