With the second wave of pandemic, the number of COVID-19 cases has been on the rise. That is why many countries or airlines started to demand negative PCR test result before boarding the plane. China went even a step further and from 6th November requires all travels to present not only negative genetic test result, but also negative test for IgM antibodies. Especially this last requirement left a lot of people confused and unsure what tests they should do. I think we should start the explanation with the types of tests that are currently available for the coronavirus.
TYPES OF COVID-19 TESTS
1. SWABS (nose or throat)
- RT-PCR – this test checks if there’s viral RNA (the genes specific for coronavirus) in your airways. Positive result means that you’re currently infected. This test is considered the most specific and the results the most reliable. It can detect the infection before you have any symptoms and is considered the golden standard of testing for COVID-19. That is why it’s also the one that is required for boarding planes. Unfortunately, this test is the most expensive and the one that takes the longest to perform. The procedure itself takes 5-6 h to get results but due to the huge rise of the number of cases around world, laboratories in many countries are swamped with samples and give out results after 2-5 days. This makes it really problematic for travellers since many places require you to do the test 48-72h before the flight. That is why before going for the test, you should confirm with the laboratory whether or not they can provide the results on time.
- FRANKED (RT-LAMP Nucleic Acid Amplification Test) – this method is new. It also checks if there’s viral RNA in the sample, but unlike RT-PCR this test takes only 30 minutes to take. They’re also half cheaper than standard tests. Unfortunately, right now they’re not widely recognized (the test has been in use for only 1-2 months so far). Hopefully in the future the testing for COVID-19 will switch to this method since it’s simply much faster and perfect for travel screening.
- ANTIGEN TEST – this test checks if there are viral proteins in your airways. It detects ongoing infection. Compared to genetic testing (PCR and FRANKED) it’s less sensitive though and is reliable mostly in symptomatic cases (people who have symptoms of coronavirus infection – for example fever and coughing). This test is very quick and much cheaper than the previous ones. It doesn’t require any special equipment. It looks a little bit like pregnancy test. You drop a few drops of sample solution in the window and after 5-8 minutes stripes will appear. This test can be done by anyone, even at home. Currently they’re often used in Emergency rooms, to quickly screen patients before admitting them to the hospital.
- IgM – it’s the early phase antibody. When your body meets with a new pathogen (in this case COVID-19) it has to learn how to recognize it. This process takes around one week. After this time white blood cells start to produce IgM antibodies. If you test positive for IgM it means you have an ongoing infection. That is why that is the type of test currently required for the travel to China. My guess is that this requirement was implemented in order to reduce possibility of false negative PCR test results (in other words to confirm that your negative result really is negative). You can test positive for IgM even up to 4 weeks after infection. They disappear after that time.
- IgG – those are memory antibodies. They’re more mature and more specific than IgM. Their level peaks around 3-4 weeks after infection, but they can stay for months. To put it simple they become your immunological memory and can protect you from getting infected again (how long this protection lasts, and how strong it is in case of COVID-19 is still unclear).
Methods of testing for antibodies:
- Rapid Cassette Test – it also resembles pregnancy test. You put a drop of blood in the window and after few minutes, stripes will appear. It can be done by anyone, even at home. This test is cheap and very quick, but not very specific. Sometimes it can give false positive results if you have common cold.
- ELISA – it’s more specific and more reliable than cassette test. It can tell you not only that you have specific covid-19 antibodies, but also how much of them. It requires special equipment. The test itself takes 1-2h but again, depending on the number of samples, you might wait up to two days for the results.
Tests for China:
From November 6th in order to board a plane to China you’ll need two types of tests:
- PCR – this test is the bottleneck of those testing because it takes long and many laboratories are too busy to provide results within 24h. Check at tour country’s Embassy of China webpage for the list of approved laboratories. Make sure that they can provide the results within 24h (you’ll need some time for the test result to be approved by the embassy).
- IgM – it’s fastest to do the cassette test. The result should be the same day. Since those tests tend to turn some false positive results if you want to be on the safe side you can also order standard (ELISA) antibody test. Time window for testing is very short, so it might be better to do both of them, just in case one is too late or the other false positive.
In most places the swab and the blood test can’t be done in the same testing side. Why? Because the swab and the blood test have different level of biohazard. The swab (PCR) is done for people potentially infected. Which means anyone who goes for this test can have the coronavirus. Since it’s a high biohazard testing point the nurses have to be in a full hazmat suit. Blood tests are done for people without symptoms, so at least in theory, healthy ones. Blood test doesn’t require full ‘space’ suit because biohazard is lower. The point of separating those testing sides is to prevent potentially COVID-19 positive patients from mixing with the healthy ones.
What does it mean for you?
In most cases you’ll have to go to two different places for those tests. It’s better to start with PCR because it takes longer and there are fewer places (only specially designated points). Antibody test can be done practically by any laboratory that does regular blood tests. The results are also faster.
Good luck! With all that’s going on now, you might need it 😉