Rapid Antigen Test Kits
The use of rapid antigen and antibody diagnostic test kits is becoming more and more common in the detection of COVID-19. These kits prove to be less expensive and faster than real-time polymerase chain reaction (RT-PCR) tests given that they provide accurate results within minutes and their procedures do not require laboratory testing.
There are two main types of rapid diagnostic testing regarding the detection way of COVID-19. First, a rapid antibody test enables the identification of immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies specifically produced by the metabolism of individuals in response to SARS-CoV-2 specific antigens. IgM antibodies are the earliest antibodies in COVID-19 infection thus at the beginning of the disease they are detectable. IgG antibodies appear later in the blood and stay in your blood long after the COVID-19 infection goes away. Thus, the result of these immunoglobulin detection tests indicates whether the person was previously infected, is currently infected, and has since recovered.
On the other hand, a rapid antigen test (RAT) enables the identification of SARS-CoV-2 specific antigens within the selected specimen. Unlike rapid antibody tests, rapid antigen tests only detect if the person has an active COVID-19 infection. The result of the rapid antigen tests does not inform us on potential prior infections or the person’s level of immunity against the SARS-CoV-2 virus however they can be useful weapons for controlling the spread of the COVID-19 pandemic.
Rapid antigen tests
Rapid antigen tests (RAT) refer to quick point-of-care (POC) diagnostic tests which are commonly used for the detection of the viral antigen presence of virus of interest for example human immunodeficiency virus (HIV) testing. Currently, the virus of interest becomes SARS-CoV-2, which causes COVID-19. These lateral flow immunoassay devices are able to identify a current COVID 19 infection from 2-4 days after the initial exposure to the virus or before the onset of symptoms.
The portable single-use sample collection device eliminates the need for laboratory testing, moreover, the results are available within 10 to 30 minutes. While molecular testing like real-time polymerase chain reaction (RT-PCR) tests remains the most accurate technique in terms of accuracy, large scale to pandemic levels is extremely difficult due to their requirements for both lab environment and lab equipment. Rapid antigen test kits, therefore, are generally less expensive and quicker than molecular or real-time polymerase chain reaction (RT-PCR) tests. These strong advantages, provide governments to control the COVID-19 pandemic likewise in the case of Slovakia.
On how rapid antigen tests work
The principle behind the working mechanism of rapid antigen tests is simple. If the collected sample has SARS- CoV-2 antigens, during the test, these antigens attach to the nanoparticles covered with SARS-CoV-2 antibodies contained within the reactive test strip. This reaction induces a colored line on the test cassette, reveals the presence of COVID-19 specific antigens within the specimen, as a consequence, indicates a positive result.
Types of rapid antigen tests
There are four groups of rapid antigen test kits basically based on what tissue the samples are collected from nasopharyngeal, nasal, oropharyngeal, and saliva. While the first three groups require a swab for sample collection, there is no need for the swab to collect a sample for the saliva optioned test kits. The usage of these test kits is summarized basically in the following paragraphs.
How to use antigen test kits?
The nasopharyngeal samples are collected by inserting a sterile cotton swab into the nostril and rubbing it inside the nose, nasal samples are collected by inserting a sterile cotton swab into the nostril again but instead the rubbing it inside the nose, it is needed to smear only 2.5 centimeters. By rubbing the swab on the tonsils you can collect oropharyngeal (throat) samples. Later, insert the swab into an extraction buffer tube. On the other hand, saliva samples are collected into a sterile package without swab usage. By using Pasteur pipette saliva is transferred to the extraction buffer tube which is already filled with extraction buffer.
Test Procedure and Interpretation
The test procedure is the same for all sampling types, to clarify, they differ only in the term of sampling. The sample contained within the tube is applied onto the test cassette. After that, the results of the test should be available within 10 to 30 minutes. The validity of the test is confirmed by the presence of the quality control line (C) on the test strip. If the C line is absent or it takes longer than 20 minutes to appear, this indicates that the test results are invalid. Indeed, if the result is negative, only the control (C) line should appear. However, if the result is positive, the antigen detection line (T) should appear along with the control (C) line.
The early diagnosis certainly plays an essential part in the monitoring of many illnesses and disorders such as tumors, cardiac issues, and blood and urinary abnormalities. Regarding the COVID-19 pandemic, it can be simpler to identify the SARS-CoV-2 quickly by screening the rapid antigen testing between groups in order to quickly triage the symptoms and asymptomatic patients and to decrease overall infectious transmission.
Thus, screening by rapid antigen test kit might be a crucial factor in the isolation of positive COVID-19 cases, eventually reducing the transmission of the virus in crowded sites, such as schools, houses of worship, bureaus hospitals, clinics, laboratories, airports, hotels, restaurants, production facilities, and community activities. Rapid antigen testing can also be useful to screening in rural regions with difficult access and in districts with poor access to healthcare.
Comparison of antigen test kits with other tests
Rapid antigen test kits have advantages such as that they require less time and money and that they do not need extra device or laboratory equipment unlike polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA) tests. In conclusion, you can find the summary table for comparison of polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA), antigen, and antibody testing below (See Table1).
Table1. comparison of test types using for COVID-19 diagnosis.