The Difference Between PCR Tests, Antigen and Antibody (IgG/IgM) Tests
Last Reviewed: 2nd October 2020
This tests for the presence of viral RNA on swabs. Results take 1-3 days to come back
While it is still considered the gold standard for accurately detecting the presence of any coronavirus, it is not the best test for accurately assessing infectiousness. PCR tests often pick up the presence of viruses well after the levels have dropped below infectious levels
Also with results not being available until at least the next day (at best) it means that you may be infecting others while you wait.
PCR tests remain the only tests accepted by airlines and immigration purposes – although this may change so it is worth checking with your destination’s immigration information regularly.
A PCR test looks for the presence of the RNA of the virus itself. It is 100% sensitive if there is virus on the swab whether someone has symptoms or not. So long as there is RNA of the virus present on the swab it will be reported as "detected".
NB: This test only picks up whether there is virus on the swab that is delivered to the laboratory. This means that in real-world terms the sensitivity of a PCR swab test ranges from 70% at worst to 95% at best. This is because swabbing technique can miss the virus.
Rapid Antigen Test - 15 minutes
These tests detect viral protein fragments and return results within 15 minutes.
This test is ideal for quickly checking whether people are infectious and at risk of spreading the virus. Perfect for workplaces, film sets and any other situations where it is important to regularly check whether people are going to be spreading the virus to anyone else.
The Abbott Panbio Antigen Rapid Test that we use has shown a 98.2% sensitivity in detecting viral levels that are currently considered to be infectious (Ct values < 33). It has an overall sensitivity and specificity agreement with RT-PCR results of 97.9%
With results available in 15 minutes it is possible to know very quickly whether your people are likely to be infectious which is the most important information needed to reduce the spread of the virus and keep people safe from being infected.
IgG Antibody Tests
This tests your blood for the presence of antibodies that your body has produced in response to being exposed to the virus. The gold standard IgG antibody test is the PHE evaluated, FDA EUA approved reagents we use, millions of which are being used by the NHS here and the rest of the world to be used in the frontline of detecting the spread of SARS-Cov-2 coronavirus through our communities.
The test has so far been shown by the FDA to be 100% sensitive in detecting antibodies 14 days after first symptoms and subsequent testing by the PHE have shown a 96% after the first symptoms of confirmed SARS-CoV-2 infection but it is not yet known whether antibodies definitely do give immunity and if they do, for how long. So do not throw away the hand gel and the face masks and start hugging people!
IgM Antibody Tests
This tests your blood for the presence of IgM antibodies that your body has produced in response to a recent exposure to the virus. This test is considered to have high sensitivity to the virus if taken at about 30 days after exposure. IgM antibodies levels drop off much more quickly than IgG levels after exposure so if your illness (or exposure) was months ago then it is the IgG you need. To travel to China you will need an IgM and a PCR test and certificate.
If you want to know:
- if you are carrying the virus in your nose and throat at any level
- if you are going to be allowed to travel to many restricted countries
Then it is the PCR test which you should have.
If you want to know:
- if you or your team are infectious right now
- if you need results quickly
Then it is the Abbott Panbio Antigen Rapid Test that you need.
If you want to know:
- if the fever and/or illness you had greater than 14 days ago - and months later - was likely to be covid-19
Then it is the IgG antibody blood test you need.
If you want to travel to China or want to know:
- if the fever and/or illness you had about 30 days ago was likely to be covid-19.
Then it is the IgM antibody blood test you need.