What are the different types of testing available?
PCR (polymerase chain reaction) testing is the most sensitive test that is currently available, it is able to detect active infection some days before the patient is infectious or symptomatic. it looks for genetic material from the virus and is generally a more sensitive test than others available.
It is seen as ‘the gold standard’ these, and used in the NHS daily. PCR testing has a turnaround time of up to 48 hours. It is performed in machines that cycle through different temperatures. As the process of changing temperature takes some time, the process is longer than other processes such as LAMP.
LAMP Testing is another form of genetic test, able to detect the RNA of the virus. It is a more recent development than PCR and is performed all at one temperature. It is generally faster and cheaper than PCR but is not considered to be as sensitive – but is still more sensitive than antigen testing. LAMP tests might be able to detect patients immediately before symptoms are displayed but this is unsure at present. Rapid LAMP testing can add a significant degree of confidence if performed before flying, for example, when all aboard have had a LAMP test prior to departure.
Antigen Testing is the fastest and cheapest of all lab tests for COVID-19. Unlike PCR and LAMP, the genetic material of the virus is not searched for, but rather the protein structures on a virally infected cell produced by COVID-19; usually the so-called ‘spike’ protein. Antigen tests often become positive after having had symptoms for a couple of days. Their use is particularly powerful when patients are attending communal events and a quick check needs to be performed to see if attendees are infectious with COVID-19. Furthermore, during winter months, when people often have symptoms of the common cold or flu, performing an antigen test will ascertain whether the condition is the coronavirus or not.
Antibody tests: When we get infected with COVID-19, our bodies make antibodies to fight the infection. The antibody test looks for the presence of these antibodies, which usually mean that we have been infected with COVID-19 in the past. This test uses a finger-prick blood test.
Read on if you want more science info…
PCR (polymerase chain reaction) test, is the most common form of testing in the UK and is seen as fairly reliable. A swab is taken from the back of the throat or the very top of the nostrils. Both are highly uncomfortable. The sample is sent to a laboratory to detect genetic material in the virus called RNA (the nucleic acid that converts DNA into proteins). RNA is collected as it carries the genetic information of coronavirus.
It is a time-consuming process involving a solution (aka reagent) which is added to the sample and then processed through various temperature steps in a thermal cycler so that it multiplies into larger quantities of DNA. Bioscientists can then see whether the SARS-CoV-2 virus (the virus that causes COVID-19) is present.
It takes around 12 hours which is why results take so long to be issued.
“LAMP” (loop-mediated isothermal amplification) tests uses a swab to collect material from the throat and nose but this is not processed in a thermal cycler. It produces many more viral RNA copies without the need to heat and cool – a constant temperature is used.
The samples are then placed in vials of reagents (substances that produce a chemical reaction to detect the RNA), then heated in a special machine for 20 minutes. The sample is analysed to confirm the presence or not of SARS-CoV-2 RNA.
What are the limitations to LAMP Testing ?
LAMP is less versatile than PCR, the most familiar nucleic acid amplification technique. LAMP is useful primarily as a diagnostic or detection technique, but is not useful for cloning or many other molecular biology applications enabled by PCR. Because LAMP uses 4 (or 6) primers targeting 6 (or 8) regions within a fairly small segment of the genome, and because primer design is subject to numerous constraints, it is difficult to design primer sets for LAMP “by eye”. (Wiki)
What is an Antibody test?
Antibody tests are used to detect antibodies to the COVID-19 virus to see if it’s likely that you have had the virus before.
The test works by taking a blood sample and testing for the presence of antibodies to see if you have developed an immune response to the virus.
Antibody tests differ to virus swab tests, which test to see if you currently have the virus. An antibody test cannot test if you currently have the virus.
There is no strong evidence yet to suggest that those who have had the virus develop long-lasting immunity that would prevent them from getting the virus again. (source GOV.UK)
What is a Lateral Flow test?
Lateral flow is an established technology, adapted to detect proteins (antigens) that are present when a person has COVID-19. The best-known example of a lateral flow test is the home pregnancy test kit.
The test kit is a hand-held device with an absorbent pad at one end and a reading window at the other. Inside the device is a strip of test paper that changes colour in the presence of COVID-19 proteins (antigens).
How to take the Test
Taking a lateral flow test usually involves taking a sample from the back of the throat near the tonsils and from the nose, using a swab.
The swab is dipped into an extraction solution. This is then dripped on to the device’s paper pad, producing the reaction that gives the result.
The result will be visible on the device precisely 30 minutes after the sample is applied. Unlike a PCR test, there is no need to send the sample to a lab.
What a Lateral Flow test cannot tell you.
- if you’re immune to coronavirus
- if you can or cannot spread the virus to other people
There is a different test to check if you have coronavirus now.
Whatever your antibody test result, you must continue to follow the same guidelines as everyone else to protect yourself and others from the virus.
How sensitive are the Lateral Flow & PCR tests?
PCR and lateral flow have different roles to play in controlling the virus, so it isn’t helpful to directly compare them in terms of how sensitive they are:
- Lateral flow is useful for finding out if a person is infectious now, and able to transmit the virus to others. The level of sensitivity is high enough to detect the vast majority of these cases. Lateral flow testing is less likely to return a positive result outside the infectious window.
- PCR is useful for confirming a suspected case of coronavirus, where the person is already self-isolating and is showing symptoms. Higher sensitivity of PCR means it can identify genetic material from COVID-19 even after the active infection has passed.
The different levels of sensitivity are therefore appropriate for the ways they are used.
How accurate are Covid tests?
Tests are never 100 per cent accurate, and vary in their “sensitivity” and “specificity”.
Sensitivity means the proportion of carriers of the virus who are correctly identified;
specificity refers to the proportion of non-carriers who are correctly identified.
So 100 per cent sensitivity would mean no false negatives, while 100 per cent specificity means no false positives.
What is the Test to Release scheme for International Travellers ?
From 15 December 2020, international arrivals are able to opt in to ‘Test to Release’.
Test to Release is a scheme to allow travellers to be released from quarantine early after taking a COVID test when they return from a UK Gov RED country (a country not on the travel Corridor list). The test should be booked before the traveller arrives home and can be carried out at one of the Collinson drive through test centres.
More info on the scheme can be found here: https://www.gov.uk/guidance/coronavirus-covid-19-test-to-release-for-international-travel
By law, all tests used for the purpose of shortening the self-isolation period for international arrivals must meet certain minimum standards.
Read more: https://www.thetravelmagazine.net/qa-what-is-the-difference-between-a-covid-pcr-test-and-a-lamp-test-for-coronavirus.html#ixzz6kOHLglhR
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