Covid Holiday: What is the difference between immunochromatography and PCR coronavirus testing? And how do they work?

Travel agency Government plans for people returning from foreign holidays Perform “expensive and unnecessary” PCR Coronavirus test.

The plan is that post-arrival testing is considered to be more accurate, but should be of the more expensive polymerase chain reaction (PCR) type.

PCR tests are different from immunochromatography (LFT). Widely used in schools In each place.

So what’s the difference between them?

The polymerase chain reaction (PCR) test is often considered a “gold standard” test to identify clinical cases of infection because it requires laboratory analysis.

PCR is a diagnostic test that detects viral RNA (genetic material) in samples taken from cotton swabs in the nose and throat.

Add substances, known as “reverse transcriptase” and “DNA polymerase”, to a cotton swab to make a copy of the viral RNA that is present.

A copy of the RNA is picked up by a “primer” that indicates that the genetic material has been found.

These are also swab tests, but immunochromatography is an antigen test, so it’s completely different.

Rather than detecting the genetic material of the virus, LFT detects the coronavirus-specific protein in the sample to detect whether people carry the virus.

LFT does not require laboratory analysis, so it returns results faster (usually within 30 minutes) and works like a pregnancy test.

Since PCR samples need to be sent to the lab, it often takes 24 hours to 3 days for the results to be returned.

PCR tests are more expensive because of the analysis required to return the results.

However, the ABTA, Travel Association, and Airport Operators Association have also found that the cost of PCR testing in the UK is twice that of tests available in other European countries.

The cost of pre-departure PCR testing in the UK is said to average £ 128 per person, compared to just under £ 62 at eight major destinations in Europe.

This means that people traveling from the UK to Europe will pay an average of £ 306 to leave the UK and return from their destination. New signal system..

LFTs are inexpensive, around £ 6 to £ 7 per test, and, like pregnancy tests, return positive or negative results in minutes and are easy to perform at home.

In the UK, the government offers free LFT to encourage people to get Tested twice a week as part of the roadmap from the blockade..

Health Minister Edward Argar said the costs will be covered by a two-year £ 37 billion NHS test and trace budget.

Some scientists have expressed concern that rapid LFT is not as effective as PCR testing, especially if people are doing LFT at home instead of being done by a healthcare professional.

Public Health England (PHE) states that when trained laboratory scientists collect cotton swabs, Innova’s immunochromatography sensitivity is 79.2%, medical professionals 73%, and track and trace center staff. We found that it was only 57.5% when used.

However, PHE said this should improve as regular mass testing increases and people test themselves on a regular basis several times a week.

The World Health Organization (WHO) also points out that the accuracy of LFT can be affected by the time from the onset of infection and the concentration of virus in the specimen.

LFT can detect positive cases, usually 1-3 days before the onset of symptoms and the first 5-7 days after the onset of symptoms, when the viral load is highest and the patient is the most infectious. It states that it is highly sexual.

This may mean that LFT is not very effective in detecting the virus in asymptomatic people.

“On average, the viral load peaks in asymptomatic people appear to be lower than the viral load peaks in symptomatic people, and they stay at that peak for less time,” said a former public health officer in the South. The director, Mike Gill, said. East of England said.

However, PCR tests can more accurately detect viruses in people who do not display the system.

Alexander Edwards, an associate professor of biomedical technology at the Leading School of Pharmacy, said:

“Therefore, it may be better to find a” spreader “than to identify everyone infected. “

However, according to the British Medical Journal (BMJ), the PCR test is also not complete.

It is said that viral shedding can be detected long after the infection period, and people continue to be positive for an average of 17 days.

“This means that non-infectious people can be unnecessarily quarantined,” he said.

There are reports that school children tested positive for LFT Only if the PCR test returns a negative..

Scientists say that neither test is error-free, but the “sensitivity” of the PCR test reduces the likelihood of false positives and false positives.

Last year, the Emergency Science Advisory Group (SAGE) stated that both false-negative and false-positive rates for PCR were unknown, but “inefficient sampling, laboratory contamination, sample degradation, or Causes of other errors “.

Last month, the government said immunochromatography tests resulted in less than one false positive for every 1,000 tests, and analysis showed 99.9% specificity.

According to the Ministry of Education, if a student’s LFT was filmed under supervision, at a test center, or at school, “there is a minimal chance that it will be incorrect, so no further testing is needed to confirm the results.” ..

However, if you test at home, the positive results are “slightly more likely” to be wrong and should be confirmed by PCR.

According to the BMJ, Jon Deeks of the Institute for Applied Health, University of Birmingham estimates that false positives in immunochromatography at low prevalence of infections mean that up to half of positive tests can be false. did.

“”[It] This week, children, teachers, families, and half of their bubbles seeking quarantine will show that they are doing so unnecessarily. “

LFT is free for anyone with or without symptoms.

These tests are available at the following URL: Local hub, pharmacy, Some workplaces and home kits Order online..

PCR tests are provided free of charge by the government for those who are symptomatic, who have come into contact with people who test positive, essential workers, or who have been asked to be tested by a GP or hospital. I will.

Register to self-reference the PCR test Here For home tests and reservations at the walk-in center.