Rapid, point-of-care antigen testing is helpful for detecting coronavirus disease 2019 (COVID-19) in symptomatic persons, according to the results of an updated comprehensive analysis published in the Cochrane Database of Systematic Reviews. However, test accuracy varies significantly between brands, and only a few exceed the World Health Organization’s (WHO) minimum acceptable performance guidelines.
Rapid detection of severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) infections is critical for optimal public health and patient outcomes. While fast point-of-care tests can not assess illness severity, rapid detection can aid clinical decision-making.
Because public health measures for COVID-19 are aimed at preventing disease transmission, clinicians’ ability to rapidly and effectively identify and isolate patients with SARS-CoV-2 infections is critical. Therefore, the current study examines SARS-CoV-2 disorder as a target condition for symptomatic and asymptomatic testing. The authors defined included tests as those that could be conducted “at the ‘point-of-care’ or in a ‘near-patient’ testing role.” The following criteria apply to point-of-care testing:
Portability or ease of transporting the equipment necessary to conduct or read the essay;
Minimal sample preparation is required, and no additional equipment or accurate sample volume transfer is needed unless a disposable automatic fill or graduated transfer device is utilised.
Biosafety requirements are minimal, including personal protective clothing for the sample collector and operator, adequate ventilation, and waste disposal in a biohazard bag;
There is no demand for a climate-controlled environment;
Within two hours of sample collection, test results are available.
129 rapid antigen and 142 automated molecular tests were commercially available outside of a laboratory environment at the time of the review. The review includes 64 publications containing data from 78 research populations examined using point-of-care COVID-19 testing; 48 of these reports evaluated antigen tests, while 29 reported on molecular tests.
What are the various diagnostic tests for COVID-19?
In contrast to antibody testing, which seeks prior infection, COVID diagnostic tests look for active infection with SARS-CoV-2, the virus that causes COVID-19.
A brief outline of their distinctions
Because the samples are gathered similarly for both types of tests, the primary distinction is the way they are processed.
While molecular tests are often more accurate and performed in a laboratory, which takes time, antigen testing—or “quick tests”—can be processed almost anywhere, including at home, in doctors’ offices, or pharmacies. As a result, antigen test results can be obtained in about 15 minutes, although they are typically less reliable.
Molecular tests are frequently employed by health care practitioners, mainly when persons exhibit COVID-19 symptoms. In contrast, antigen testing is commonly used when rapid results are required or for general screening and surveillance.
Investigating genetic evidence
For any type of test, the initial step is to obtain a sample from the patient. This can be a swab of the nose or small saliva.
For PCR tests, the following step is amplifying the genetic material. Which allows for detecting even a minute amount of coronavirus genes in the patient’s sample. This is accomplished by using a process known as a polymerase chain reaction. A health care expert creates double-stranded DNA after a sample is taken and an enzyme is used. Heat and an enzyme are known as polymerase cause the DNA to split into two single-stranded pieces. Which are subsequently used in the cloning process. Polymerase binds to and duplicates the single-stranded DNA with the help of a short piece of guide DNA called a primer when the temperature is lowered. Coronavirus-specific primers are used in this experiment. The second round of replication of coronavirus DNA has now taken place.
Laboratory machinery performs these heating and cooling cycles 30–40 times, doubling the DNA to a billion copies. Finally, the amplified sequence is labeled with a fluorescent dye that a machine can read.
Due to the amplification ability of PCR, even the tiniest quantity of coronavirus genetic material in a sample can be detected successfully. As a result, it is a susceptible and accurate test. It is the gold standard for diagnosing SARS–CoV–2 because of its near-perfect accuracy.
However, PCR testing has several limitations. The entire amplification process can take an hour or more. Generally, only extensive, centralised testing facilities – such as hospital laboratories – can perform several PCR tests concurrently. A person should expect to wait between 12 hours and five days for findings between sample collection, transportation, amplification, detection, and reporting. Finally, they are not inexpensive, costing $100 or more per test.
Antigen examinations
Rapid and precise testing is critical for the containment of a highly contagious virus such as SARS-CoV-2. While PCR tests are accurate, they can take a long time to complete. While antigen tests, the other primary form of coronavirus, are significantly faster, they are also considerably less accurate.
Antigens are substances that elicit an immunological response in the body — they initiate the production of antibodies. These assays look for antigens from the SARS-CoV-2 virus using laboratory-made antibodies.
To conduct an antigen test. A sample is first treated with a solution containing salt and soap. Which dissolves cells and other particles. Then you add this liquid to a test strip coated in a thin line with antibodies specific for SARS-CoV-2.
Like those in your body, antibodies on the test strip will bind to any antigen in the sample. For example, if the antibodies recognise coronavirus antigens, a colored line indicates the presence of SARS-CoV-2 on the test strip.
Advantages
Antigen tests possess a variety of advantages. First, they are so simple to do and interpret that they may be performed and interpreted by someone with no special training – even at home. Additionally, they produce effects swiftly, generally within 15 minutes. Another advantage is that these tests are relatively inexpensive, costing between $10 and $15 per test.
Disadvantages
Antigen tests do have a few disadvantages. They may be less accurate than PCR testing in some circumstances. Antigen testing is highly accurate when a person is sick or has a high level of virus in their system. However, unlike molecular PCR testing, antigen tests do not amplify the target. This means that the sample must have sufficient viral antigen for the antibodies on the test strip to give a signal. When a person is in the early stages of infection, a little virus in the nose and throat is used to obtain the samples. As a result, antigen screenings may miss early COVID-19 instances. Additionally, because a person has no symptoms during this stage, they are more likely to be unaware they are infected.
These tests can determine whether a person has had a previous COVID-19 infection but not whether they are still positive for the virus. Tran stated that antibody tests might become more valuable once an effective vaccination becomes available.
