1. Lack Of Resources
With the entire world hunting for the same testing resources at the moment there is a severe shortage. It’s important that we spend the testing resources we do have on those who need a diagnosis as priority. If a high risk individual is presenting with symptoms of COVID-19 we need a diagnosis to know the right course of treatment and to trace anyone that may have caught it from this individual to stop further spread.
Right now in the UK the NHS are using PCR tests to test for the positive diagnosis of COVID-19. These work by identifying the virus DNA in a swab of a patients’ saliva & cells taken from the back of their throat (nasopharynx). It takes between 4 and 24 hours to get a result and requires specialist equipment, but is very effective at identifying the virus in small amounts at early stages of infection. It is logistically impractical to roll out this kind of testing to everyone and important we keep testing capacity for vulnerable patients and key staff. Currently around 10,000 PCR tests are being done per day.
Antibody tests are an alternative. Rather than looking for the virus itself these look for the body’s response to the virus. If your body is fighting the virus it will produce SARS-CoV-2 ‘antibodies’ in the blood which work to destroy the SARS-CoV-2 virus (the cause of COVID-19 sickness). The benefit of this is that the antibodies give an indication of how recent your infection was and, importantly, if you are now showing immunity. (We don’t know how long SARS-CoV-2 immunity will last yet, look out for a future article on this topic.)
The antibody tests can deliver results in as quick as 10 minutes from a simple finger-prick blood sample, are far cheaper than the PCR tests and don’t need any specialist lab equipment. The downsides are that they are only effective from 7 days after infection as it takes time for the antibodies to form in the blood, and they’re only around 95% accurate at the moment. (See our article on Sensitivity & Specificity)
However, this is a scalable solution. So why aren’t we doing it?
2. It Wouldn’t Actually Help
Testing everyone is a pointless exercise at the moment.
The vast majority of the population have not had the virus, current estimations put it between 300-400k or roughly 0.5%. We’ve only been able to confirm 65k cases in hospitals (as of Friday 10th April 2020). If we were to test the entire population on this basis with a test accuracy of 95%, the 5% of erroneous results could represent as many as 3.2million people. i.e. more false positives than true positives
If you have not had any symptoms of COVID-19, nor been in close contact with anyone that has, then it’s currently unwise to test yourself. You’re far more likely to receive a false positive result for virus immunity and risk putting yourself in harm’s way when you could still be vulnerable.
However, using antibody tests to test anyone that has or has had symptoms, or has been in close contact with those that have, is the right thing to start doing now. Antibody tests can take some of the pressure off overstretched PCR test resources. Realistically it’s the only way the Government will reach their target of 100,000 tests per day.
The UK Government will likely announce the start of these measures in the next couple weeks, but they will only do so when they’re confident of high test accuracy.