Antibody detection test for COVID 19 and its relevance

As the country goes into unlock mode, it is imperative to point out that “Caution is the need of the hour.”  In cognizance of this the ICMR in its advisory dated 23/06/2020, validated and approved the use of IgG ELISA antibody against COVID -19 for surveillance of state of immunity of individuals and community. The Delhi government too allowed Public sector units, government offices, businesses corporate, agencies, health care workers and organisations planning to reopen business to engage private labs to conduct ELISA (IgG) antibody test to check for immunity against SARS COV2 amongst their employees. They feel this will help in allaying anxiety and fear, both amongst the workers and the consumers. According to some media reports, this is a part of ICMR’s “Immunity Certified Plan” which would allow asymptomatic individuals positive for IgG antibodies to resume usual activities.

At Tomar Foundation Pathology Lab, we are testing Antibody(IgG) to COVID19  to aid in this government endeavour. However, I find that there is a lot of confusion regarding this test and its relevance amongst the general public. In this article, I will attempt to answer the FAQ’s and provide clarity and information on this topic.

 

What is relevance of Antibody (IgG) detection test against COVID 19?

This is an ELISA test for detection of presence of IgG antibodies against SARS COV 2 in the blood. IgG antibodies start appearing after 2 weeks of onset of infection and last for several weeks to months. Many studies have stated that the load of asymptomatic people who have suffered from COVID is at least ten times the official figure. This test is highly useful in identifying people who have suffered from the disease and gained immunity on the quiet.

As IgG antibodies have no role in acute infection, this test has no diagnostic value at the time of acute infection. The presence of IgG antibodies in asymptomatic individual indicates

• Previous exposure to the Corona virus
• Development of immunity to SARS COV2
• IgG positive person can donate plasma.
• Provides a break in transmission chain in the community

When should the test be done?

• The test can be done at any time in asymptomatic individuals.
• In people who have had the disease or had direct exposure to exposure to COVID positive people, it should be done 3 weeks after exposure.

 

Who should get themselves  tested?

According to ICMR, the following populations should get themselves tested

• Employers and employees at corporate houses, offices and businesses that want to open up
• Banks, post, couriers, telecom offices: public or private banks, small or large branches of banks and post, telecom offices as well as couriers;
• Migrant workers
• Industrial workers / labour force
• Health Care Workers:
• Security personnel
• Police and paramilitary personnel civil defense & volunteers
• Press corps
• Immune-compromised patients: diabetics, cirrhosis patients, cancer patients etc.
• Drivers, personal help and security guards Staff at businesses, homes and offices that want to open up
• Staff in municipal bodies: Municipal staff working in areas like sanitation, water supply, electricity, etc. where interactions with citizens is expected;
• Farmers, sellers, brokers, purchasing vendors, distributors and other persons including drivers and labour by virtue of visiting crowded places like main markets
• Drivers of hospital ambulances, hearse, buses, auto, taxies, etc. Bus conductors, cleaners and helping staff also should be included.
• Individuals who have been on work front and faced large number of people previously or are going to face in future.
• Individuals in containment zones
• Vendors and/ or owners as well as staff working in shops

How reliable is this test?

The reliability of the test depends on the reliability of testing kit used. It is pertinent that the laboratories conducting the test use only ICMR approved kits. ICMR has recommended only IgG (ELISA) test kits for reliable testing. The kit has a sensitivity of 98.3% and specificity of 98.1%.There is low false positive and false negative due to high specificity and high sensitivity.

 

Are Rapid tests for Covid 19 reliable?

ICMR has banned rapid tests for Covid 19 due to their unreliability. These tests have gained a lot of notoriety world over.

 

Is a person with IgG antibody 100% immune to re-infection?

The influenza virus is well known for its propensity to transmutate and change structure. So, a person with IgG antibody may get infected by a new strain of virus. The new strain of virus is still going to be structurally close to the other strains. Thus, he would be better equipped to fight the infection as compared to a person with no antibodies.  Let us not forget,”Small pox was eradicated using a Cow pox vaccine.”

Also the person’s general immunity status and presence or absence of co-morbidities would also play an important role in the scenario.

Getting oneself tested for anaemia, Vitamin d deficiency, Vitamin B12 deficiency, blood sugar levels, kidney function assessment and liver function assessments along with antibody to COVID 9 will go a long way towards preventive care. TFPL offers Basic Immunity profile and Comprehensive Immunity profiles to help allay your anxieties.

 

Author:
Dr Vibha Tomar
Consultant Pathologist
Tomar Foundation Pathology Lab