What is the Difference Between Antigen and NAAT Test

The key difference between antigen and NAAT test is that antigen test is a diagnostic test that detects the presence of specific antigens in infectious agents, while NAAT test is a diagnostic test that detects the nucleic acid sequence of infectious agents.

Antigen and NAAT tests are two different types of diagnostic tests to detect infectious agents in infectious diseases. Antigen tests are less sensitive than NAAT tests. Therefore, a negative antigen test result should not be used to rule out an infection. A negative antigen test should be repeated at least 48 hours and should be followed up with a NAAT test to confirm the results from the antigen test.

CONTENTS

1. Overview and Key Difference
2. What is an Antigen Test
3. What is a NAAT Test
4. Similarities – Antigen and NAAT Test
5. Antigen vs NAAT Test in Tabular Form
6. Summary – Antigen vs NAAT Test

What is an Antigen Test?

An antigen test is a diagnostic test that detects the presence of specific antigens in infectious agents. Rapid antigen test is a type of antigen test that is commonly used in the present. It is a very fast point-of-care testing. Rapid antigen tests directly detect the presence or absence of an antigen. It is also a type of lateral flow test. Rapid antigen test gives a result in 5 to 30 minutes. It also requires minimal training or infrastructure. Because of this, it is used for the detection of highly infectious and lethal pathogens like SARS-CoV-2 that causes COVID-19. Rapid antigen tests can also be used to detect bacteria such as Streptococci (rapid strep test).

Antigen tests are based on the principle of antigen-antibody interaction. In this test, antibodies directed against the target antigen are fixed to the indicator line of the chromatography substrate and visualization marker. When the sample containing antigen is added, the antigens bind with the antibodies. This allows the visual detection of a significant level of antigen in the sample. The problem with antigen tests is their low sensitivity. Therefore, test results of an antigen test should be confirmed with a highly sensitive PCR test.

What is NAAT Test?

NAAT test is a diagnostic test that detects the nucleic acid sequence of infectious agents. It is a type of nucleic acid test (NAT). It detects a particular nucleic acid sequence, consequently detecting a particular species or subspecies of an organism. Normally NAT detects viruses or bacteria that act as pathogens in samples like blood, tissue, or urine. However, the amounts of DNA generated in many NAT tests are very small. Hence, in NAAT (nucleic acid amplification test), an additional step is included that amplifies the genetic material. There are several ways to amplify the genetic material in the NAAT test: polymerase chain reaction (PCR), strand displacement assay (SDA), and transcription-mediated assay (TMA).

A NAAT test is highly specific and has high sensitivity as well. It is commonly used with rapid antigen tests for the SARS-CoV-2 pathogen. In rare cases, NAAT may also cause problems due to mutants, like nucleic acid sequences that are usually slightly different from normal nucleic acids. This leads to imperfect probe-target binding, which results in false positive outcomes, such as mistaking a commensal agent for one that is pathogenic.

What are the Similarities Between Antigen and NAAT Test?

• Antigen and NAAT tests are two different types of diagnostic tests to detect infectious agents in infectious diseases.
• NAAT is used to confirm the results of antigen tests.
• Both are extremely important in detecting infectious diseases and saving the lives of millions of people around the world.
• Both are currently used together to detect SARS-CoV-2, which causes COVID-19.

What is the Difference Between Antigen and NAAT Test?

The antigen test is a diagnostic test that detects the presence of a specific antigen of infectious agents, while the NAAT test is a diagnostic test that detects the nucleic acid sequence of infectious agents. Thus, this is the key difference between antigen and NAAT test. Furthermore, antigen tests are typically less specific and less sensitive than NAAT tests.

The below infographic presents the differences between antigen and NAAT test in tabular form for side-by-side comparison.

Summary – Antigen vs NAAT Test

Antigen and NAAT test are two different types of diagnostic tests to detect different infections. Both these tests are used concurrently in infectious studies. Antigen test detects the presence of specific antigens, while the NAAT test detects the nucleic acid sequence of the infectious agents. So, this is the key difference between antigen and NAAT test.

Reference:

1. “Guidance for Antigen Testing for SARS-COV-2 for Healthcare Providers Testing Individuals in the Community.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention.
2. “Nucleic Acid Amplification Tests (NAATs).” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention.

Image Courtesy:

1. “Covid19 Antigen Rapid Test Kit” By dronepicr (CC BY 2.0) via Flickr
2. “PCR” By Madprime – Own work (CC BY-SA 3.0) via Commons Wikimedia