Antigen and Antibody Test

Difference Between Antigen and Antibody Test

Brief Overview of Antigen and Antibody Test

Antigen and Antibody Test are two diagnostic tools commonly utilized in medical diagnosis. Antigen tests detect viral or bacterial proteins present in the body and are useful in early identification of active infections; while antibody tests measure immune system response to infections or vaccination, and can provide insights into past exposure or assess immune status responses to vaccines or infections.

Antigen Test

Antigen tests are diagnostic tools used to detect specific viral or bacterial proteins known as antigens in an individual’s body, typically during early signs and stages of illness. Their primary application is for active infections.

Figure 01: Antigen

A standard test involves taking a nasal or throat swab sample and then testing for presence of target antigens using various techniques, such as lateral flow assays or enzyme-linked immunosorbent assays (ELISA).

Antigen tests are known for their rapid turnaround times and quick results delivery; often within minutes. Antigen tests are widely utilized when quick identification of active infections is key, such as screening programs, point-of-care testing or outbreak investigations.

Antigen tests tend to provide faster results but have lower sensitivities compared to polymerase chain reaction (PCR) tests, potentially yielding false-negatives when viral loads are low or tests taken early during an infection when adequate quantities of antigen may not exist.

Antigen tests were widely employed during the COVID-19 pandemic to screen individuals for infection by SARS-CoV-2 virus, helping identify infected individuals while taking appropriate public health steps to control its spread.

Antibody Test

An antibody test (also referred to as serological analysis) is a diagnostic procedure intended to measure antibodies present in one’s blood. Antibodies are produced by your immune system as part of its defense response against infection or vaccination, so measuring them accurately will reveal where any deficiencies exist in terms of antibody levels in blood may exist.

Antibody tests involve taking blood from an individual through a venous blood draw and then analyzing it to detect antibodies against specific pathogens like viruses or bacteria present. They can identify immune reactions against viruses as well as bacteria.

Antibody tests are used to ascertain if an individual has ever been exposed to certain pathogens or has developed immunity through vaccination, thus providing valuable data on past infections, understanding disease spread in populations and measuring effectiveness of vaccination programs.

Importantly, it should be remembered that it takes the immune system time to produce detectable levels of antibodies; acute infections typically require multiple days-weeks after initial exposure for antibodies to become visible, thus negating antibody tests as suitable ways of diagnosing active or recent infections.

There are various kinds of antibody tests, from rapid lateral flow assays and laboratory-based ELISAs, that detect specific IgM and IgG antibodies which indicate various stages in an immune response process.

Antibody Test
Figure 02: Antibody Test

Antibody tests should be considered with caution due to potential limitations such as false-positive and false-negative results and variable duration/levels of protection that depend on pathogen and individual factors.

As part of the COVID-19 pandemic, antibody tests were widely employed to ascertain prevalence rates of SARS-CoV-2 infections among individuals as well as assess immune response in them and contribute to public health strategies such as identifying possible convalescent plasma donors.

Key Differences between Antigen and Antibody Tests

There are various key differences between Antigen and Antibody Test:

  1. Biological Target:
    • Antigen Test: Antigen tests detect the presence of viral or bacterial proteins (antigens) in a person’s body.
    • Antibody Test: Antibody tests detect the presence of specific antibodies produced by the immune system in response to an infection.
  2. Timing of Detection:
    • Antigen Test: Antigen tests are used to identify active infections. They can detect the presence of antigens during the acute phase of the illness.
    • Antibody Test: Antibody tests are used to determine past or ongoing infections. They detect the antibodies that the immune system produces after the initial infection or vaccination.
  3. Window of Detection:
    • Antigen Test: Antigen tests can provide results relatively quickly, usually within minutes. They are effective at detecting infections during the early stages when the viral load is high.
    • Antibody Test: Antibody tests may take several days to weeks after infection for antibodies to be detectable in the blood. They are not suitable for early detection of an active infection.
  4. Purpose in Disease Diagnosis:
    • Antigen Test: Antigen tests are primarily used for the identification of active infections. They are useful for diagnosing individuals who are currently infected and may be contagious.
    • Antibody Test: Antibody tests are used to determine past exposure to a particular pathogen or assess the body’s immune response. They help identify individuals who have developed immunity due to previous infections or vaccinations.
  5. Use Cases and Applications:
    • Antigen Test: Antigen tests are commonly used in settings where rapid diagnostic results are crucial, such as in screening programs, point-of-care testing, or outbreak investigations.
    • Antibody Test: Antibody tests are used in seroprevalence studies to estimate the proportion of a population that has been exposed to a specific pathogen. They are also employed in assessing vaccine effectiveness and determining an individual’s immune status.

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Topic Antigen Test Antibody Test
Biological Target Viral or bacterial proteins (antigens) Specific antibodies produced by the immune system
Timing of Detection Active infections Past or ongoing infections
Window of Detection Acute phase of infection Days to weeks after infection
Purpose Identify active infections Determine past exposure or immune response
Diagnostic Stage Early stages of infection Post-infection or immune response
Sample Type Nasal or throat swab Blood sample
Turnaround Time Rapid results (usually within minutes) Results may take longer (hours to days)
Use Cases Rapid diagnostic testing, screening programs, outbreaks Seroprevalence studies, vaccine effectiveness assessment
Suitability Detects current infections, may have lower sensitivity Determines past exposure, immune status, and vaccination
Examples COVID-19 rapid antigen tests Serological tests for detecting COVID-19 antibodies


Antigen and antibody tests are indispensable tools in modern medical diagnostics. They play a pivotal role in identifying infections, assessing immune responses, and guiding public health strategies. As the world continues to face new health challenges, these tests will remain crucial in safeguarding global well-being.