Antigen And Antibody Tests
Covid, Tests & Procedures

Antigen And Antibody Tests: Differences And Uses

The body produces antibodies in response to antigens. Thus, to identify the presence of past infection, the doctor recommends an antibody test. An antigen test is for detecting the active infectious disease.

What Is An Antibody Test?

Whenever viruses or other pathogens attack the body, the immune system responds and produces chemicals for fighting against the invaders. These are known as antibodies. The doctor advises the patient to undergo an antibody test to determine the presence of these antibodies.

The immune system develops several types of antibodies at different phases of infection. These are immunoglobulin G (IgG), immunoglobulin M (IgM), and immunoglobulin A (IgA). However, immunoglobulin G (IgG) is one of the most commonly used and reliable indicators for determining current or past infectious diseases. It is because these antibodies last for a prolonged period after the suppression of infection.

When The Doctor Recommends Antibody Tests?

The use of antibody tests is only in specific cases. The doctor may advise the antibody tests if the symptoms can be linked to viral infections, although the infection may already occur weeks or months before. In such cases, the patient had tested negative for active viral infections.

People who are taking part in the research studies may also undergo antibody tests. The researchers provide detailed information to the participants about the purpose of the study. However, it is to be noted that antibody tests are not recommended for evaluating the immunity of the person against a particular viral infection. It is because there is limited information about the association between immunity and antibody levels.

What Is An Antigen Test?

Antigens are the part of pathogens that activates the immune system resulting in the production of antibodies. Any part of the bacteria or virus, such as cell wall, surface proteins, toxins, or capsule, may act as an antigen.

The antigen test is the test for identifying the presence of antigen in the body. It is an immunoassay and is generally a qualitative test. It helps in diagnosing the active infection.

When Antigen Tests Are Used?

The doctor may recommend antigen tests to diagnose the current and active infection. It also helps in the primary screening of the suspects in cases of the pandemic, such as COVID-19. After the antigen tests, the doctor usually recommends confirmatory tests. These tests are faster, easier, and less expensive as compared to other highly sensitive tests.

What Is The Difference Between Antigen And Antibody Tests?

There are several differences between the antigen and antibody test. Antigen test determines the presence of antigens, while antibody test informs about the presence of antibodies. The time for results in antigen test is generally 30 minutes, while it requires a day with antibody tests. Antigen test detects the current active infection, while antibody tests detect the past infectious diseases.

How The Antigens And Antibodies Are Used In Vaccination?

The primary purpose of vaccines is to develop antibodies in the body for a particular disease or pathogens. The vaccines contain the inactive part of the disease-causing organism. When injected into the body, it activates the immune system. The immune system then forms antibodies against the antigen. In some cases, the vaccines are needed to be administered multiple times with a gap of a few weeks or months. It helps the body to maintain antibodies for a longer period. The antigen is inactivated or weakened and thus does not cause the disease.

How Covid-19 Is Tested Through Antigen Test?

While performing the antigen test for COVID-19, the healthcare staff inserts a cotton swab into your nostrils. The sample may be taken either from the lower part or back of your nose. The patient usually gives the sample from both the nostrils. Once inside the nostrils, the staff rotates the swab to get the required amount of sample. You may have cough or watery eyes as a reflex while taking the sample.

How Covid-19 Is Tested Through An Antibody Test?

Before the test, inform the doctor if you have taken COVID-19 vaccination or are experiencing the symptoms of the disease. For the test, the staff will tie an elastic band to the upper arm. Then he will apply the antiseptic solution to the inside of your elbow. The staff will insert the needle in the vein and draw the required amount of blood. A cotton piece is placed on the puncture site, and the pressure is applied to prevent bleeding.


Antigen test for COVID-19 requires a sample of the nasal swab, while blood is taken as a sample for an antibody test. Antigen test is a simple, faster, and easier method.