Difference Between Molecular and Antigen Test

The key difference between molecular and antigen test is that molecular test detects specific parts of the genetic material of a pathogen while antigen test detects specific protein markers called antigens present on the surface of the pathogen.

Molecular test and antigen test are two types of diagnostic tests used to detect active infections like the SARS-CoV-2 virus. Molecular tests target genomic materials specific to a pathogen or infectious agent. They amplify specific fragments of genetic materials of the pathogen. Therefore, they are molecular-based techniques such as PCR, LAMP, and CRISPR. Antigen tests, on the other hand, target protein markers on the outside of the pathogen. A molecular test for SARS-CoV-2 detects specific parts of the SARS-CoV-2 genome sequence, while an antigen test for SARS-CoV-2 detects specific markers on the outside of the SARS-CoV-2 virus.

CONTENTS

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

What is a Molecular Test?

A molecular test is a type of diagnostic test used to detect an infection. Molecular tests are based on molecular techniques, and they detect specific parts or sequences of the genetic material of the pathogen. They are also called nucleic acid amplification tests. Pathogen-specific genomic sequences verify the presence of a particular causative agent of a disease. For example, SARS-CoV-2 is a single-stranded positive-sense RNA virus. RNA of the virus will be amplified by a molecular test. If a virus is present in the sample, it will be amplified and detected at the end, confirming the presence of the virus. If present, the test is positive. If RNA is not detected, the test is negative.

Generally, molecular tests create millions of copies from a small segment of the genome. Hence, even if a small dose of virus is present, it can be detected by a molecular test. Therefore, molecular tests are accurate and highly sensitive. Polymerase chain reaction (PCR) tests, loop-mediated isothermal amplification (LAMP), and clustered, regularly interspaced short palindromic repeat (CRISPR)-based assays are several types of molecular tests.

What is an Antigen Test?

Antigen test is another diagnostic test. It detects specific protein markers on the surface of the pathogen. It is a quick test and provides results faster than a molecular test. It may take 30 minutes to days, depending on the test. Unlike a molecular test, an antigen test can be performed at the point of care, especially in a medical setting. However, in comparison to a molecular test, antigen tests have a higher chance of missing an active infection. Though an antigen test is negative, showing the absence of an active infection, a molecular test is necessary to confirm the result.

Rapid antigen test is the antigen test that is mainly used for SARS-CoV-2 at the moment in the world. It detects SARS-CoV-2 surface markers on the outside of the virus. But, it only detects the active production of viral proteins. If the viral protein production is low, it may produce a false or negative result.

What are the Similarities Between Molecular and Antigen Test?

• Molecular and antigen tests are diagnostic tests.
• They require a sample from the patient.

What is the Difference Between Molecular and Antigen Test?

A molecular test is a diagnostic test that detects specific sequences of the genetic material of an infectious agent, while an antigen test is a diagnostic test that detects specific protein markers found outside of the pathogen. So, this is the key difference between molecular and antigen test. Besides, a molecular test may take 1 to more days to give results, while an antigen test can produce results within about 30 minutes. Thus, this is another difference between molecular and antigen test.

Moreover, a molecular test is highly sensitive than an antigen test. Most importantly, a molecular test should be done in a laboratory setting, while an antigen test can be performed in a medical setting, even at the point of care.

The below infographic shows more differences between molecular and antigen test in tabular form.

Summary – Molecular vs Antigen Test

A molecular test detects the genetic material of the pathogen while an antigen test detects specific surface protein markers on the surface of the pathogen. Thus, this is the key difference between molecular and antigen test. An antigen test provides results faster than a molecular test. But, the results of a molecular test are highly accurate and sensitive than the results of an antigen test. Antigen test may produce false or negative results if the viral protein production is low though the pathogen is present.

Reference:

1. “Antigen and Molecular Tests: Types of COVID-19 Tests.” COVID-19 Testing Toolkit, 26 Mar. 2021, Available here.
2.  “Different Types of COVID-19 Tests Explained.” UC Davis Health, Available here.

Image Courtesy:

1. “COVID-19 PCR testing in Ghana” By Noguchi Memorial Institute for Medical Research –  (CC BY-SA 4.0) via Commons Wikimedia
2. “COVID-19 rapid test” By Lennardywlee – Own work (CC BY-SA 4.0) via Commons Wikimedia