Which COVID-19 test is the best?
Different tests, what they're called, how samples are taken and what they show
DUBAI: There are a number of tests for coronavirus in use today. No test, however, is 100% accurate all of the time. Numerous manufacturers have developed and begun selling “rapid” and easy-to-use devices to facilitate testing outside the lab, but health authorities like the US Food and Drug Administration have issued warnings over the accuracy of such tests, especially over "false positive" and "false negative" results.
Following are the different tests:
Molecular test
It's the most reliable coronavirus test, so far. It goes by different names: A molecular test is also known as diagnostic test, viral test, nucleic acid amplification test (NAAT), RT-PCR test, and Loop-mediated isothermal amplification (LAMP) test. It detects the genetic material of the virus. A positive result (diagnosis) shows an active SARS-CoV-2 infection. However, it cannot show if you ever had COVID-19 or were infected with the coronavirus in the past.
Sample for a moleclar test is usually taken via nasal or throat swab (most tests), or saliva (a few tests). Results for a molecular test may come the same day (in some locations) or up to a week. With a molecular test, there's usually no need for another test, as this test is typically highly accurate and usually does not need to be repeated. Downside for PCR: Relatively high cost compared to either antigen or antibody test.
Antigen test
Antigens are any substance that stimulates the immune system to produce antibodies. Antigens can be bacteria, viruses, or fungi that cause infection and disease. An antigen test, only available in certain countries, is also known as rapid diagnostic test (some molecular tests are also rapid tests.) For an antigen test, nasal or throat swab is taken. A typical antigen test detects the presence of viral proteins expressed by the SARS-CoV-2 in a sample from the respiratory tract, i.e. it diagnoses active coronavirus infection.
Antigen test results can come within minutes and is a less expensive test than a molecular test. Some experts consider antigen tests more practical to use for large numbers of people. If the target antigen is present in sufficient concentrations in the sample, it will bind to specific antibodies fixed to a paper strip enclosed in a plastic casing and generate a visually detectable signal, typically within a few minutes. But while positive results are usually highly accurate, negative results may need to be confirmed with a molecular test.
One major downside to an antigen test: It cannot definitively rule out active coronavirus infection. Compared to molecular (PCR swab) tests, antigen tests are more likely to miss an active coronavirus infection. This is known as "false negative". So if you show signs of COVID-19 and get a negative antigen test result, your health care provider may still order a molecular test.
Antibody test
Antibodies, also called immunoglobulins, are Y-shaped molecules — proteins naturally produced by the body that help fight against foreign substances called antigens.
An antibody test, in which a sample is taken via a finger stick or blood draw, is also known as "serological test", "serology test", "serology", "blood test". Results may be obtained within the same day, or in 1-3 days. A positive result shows that you've had an infection in the past. For accurate results, sometimes a second antibody test is needed. However, it cannot diagnose an active COVID-19 infection at the time of the test. An antibody test also cannot show that you do not have COVID-19.
Laser test
The UAE has pioneered a laser-based COVID-19 test, including drive-through test centres operated by Abu Dhabi’s public health provider, the Abu Dhabi Health Services Company (Seha). The laser-based technology was developed in Abu Dhabi, and is used alongside the molecular (PCR) testing protocols (the UAE introduced drive-through PCR test facilities in March).
The laser technique, known as Diffractive Phase Interferometry (DPI), looks for specific inflammation markers (viral antigens, or molecules that trigger an immune reaction) caused by COVID-19 infection in a sample. Results typically come "in seconds", or less than a 1 minute. The system uses an ultra-sensitive light-based "bio-sensors" to detect coronavirus. DPI is considered advanced and reliable enough to help in a mass screening drive.
DPI offers an advanced solution (compared to an antibody test), as it detects an active infection. This is done through a nanosensor that detects changes in the cellular structure when infected by the virus. A DPI test is useful for rapid, mass testing. In case of positive result, a confirmatory test can be done via molecular (PCR/swab) test. One downside of this DPI test is that it's not yet widely available. It's also not clear how quickly the DPI testing devices can be manufactured and how much does it cost.
287
Testing updates
As of November 2, 2020, the US FDA has authorised 287 tests under Emergency-Use Authorisation (EUAs); these include 223 molecular tests, 57 antibody tests, and 7 antigen tests. [Source: FDA]
The FDA stated that it was "aware of reports of false positive results associated with antigen tests used in nursing homes and other settings, and continues to monitor and evaluate these reports and other available information about device safety and performance.
The FDA reminds clinical laboratory staff and health care providers about the risk of false positive results with all laboratory tests. Clinical laboratory staff and health care providers can help ensure accurate reporting of test results by following the authorized instructions for use of a test and key steps in the testing process as recommended by the Centers for Disease Control and Prevention."
OTHER TESTS
There are some new diagnostic tests available with alternative methods and benefits, including:
Rapid, point-of-care test:
This diagnostic test uses a mucus sample from the nose or throat but can be analyzed at the doctor’s office or clinic where the sample is collected and results may be available in minutes. These may be molecular or antigen tests.
At-home collection test:
This is available only by prescription from a doctor. It allows the patient to collect the sample at home and send it directly to the lab for analysis.
Saliva test:
This allow a patient to spit into a tube rather than get their nose or throat swabbed. Saliva tests may be more comfortable for some people and may be safer for health care workers who can be farther away during the sample collection.
Multiple protein test:
Scientists have found 27 key proteins in blood samples of COVID-19 patients. A protein test detects the presence of such proteins in people’s blood. The proteins are present in different levels in COVID-19 patients, depending on the severity of their symptoms, say British and German scientists. This could act as predictive markers for how ill a patient could become, accordng to a study published Cell Systems in June 2020. Three of the key proteins they found were linked with interleukin IL-6, a protein known to cause inflammation. It is also a key marker for severe COVID-19 symptoms.
A test that would help medical professionals predict how ill a patient might get when infected with the new SARS-CoV-2 coronavirus would be invaluable. This could also provide new targets for the development of potential treatments for the disease.
Those infected with SARS-CoV-2, respond differently — with some developing no symptoms at all, while others need to be hospitalised and others suffer fatal infection. This type of mutiple-protein test for COVID-19 may be possible in the near future.