Today we are looking at the constantly-evolving picture of COVID-19 testing.
We will endeavour to give our opinion as to what we feel is the best approach to testing generally, while highlighting some of the pitfalls in this rather complex subject.
Antibody testing tests for the body’s immune response to COVID-19 by measuring one or two different antibodies (immunoglobulins) that the immune system generates in response to any infection. This can take from a few days, but more usually a few weeks after infection, to develop. It does not test for the disease itself.
The real value of antibody tests are from a public health perspective, allowing detailed analysis of the spread of disease in the greater population, which will be critical for leaving the ‘lockdown’ situation we are currently in.
For this to happen, the tests need to be reliable and accurate, but also organised and conducted on a large scale in a controlled way. There are further uncertainties however, as COVID-19 is a new disease:
- It is unclear as to the best time to test for antibodies. It is believed to be a minimum of 21 days post the start of any symptoms but may be longer. Testing before this time increases the risk of under-detection
- It is unclear how long the COVID-19 antibodies remain in the system. They may well disappear completely after time
- We don’t yet know whether possessing antibodies to COVID-19 affords protection to further exposure to the virus, in the medium or longer term
- We also don’t know whether any immunity will be present against newer variants or ‘mutations’ of COVID-19
- It is very likely people who suffer a mild or asymptomatic disease may generate a much smaller antibody response, again resulting in under-detection
Home and ‘finger prick’ tests
These are new tests produced by an ever-increasing number of manufacturers globally. The rush to get these to market has meant the usual stringent validation and approval that would normally apply to any medical device, simply has not occurred. The ‘test of the test’ has not happened, which has led to growing uncertainty on their validity.
We heard from health secretary Matt Hancock that the government had ordered around 18 million such tests from a Chinese manufacturer. On further analysis by Oxford University, they were found to be inaccurate, with a very real risk of false negatives.
This has huge ramifications in safety terms, particularly for those wanting to know COVID-19 status prior to caring for an elderly or vulnerable relative or friend.
No test is ever 100 per cent accurate, but there are certain scientific thresholds that need to be achieved to make it at all useful.
The body that regulates medical devices in the UK, the Medical and Healthcare Products Regulatory Agency (MHRA), has since published its first guidance on the ‘acceptable’ and ‘desirable’ standards that any approved finger-prick test should meet.
Unsurprisingly, these are very rigid and set the bar rather high. This will result in further tests being rejected for falling well below these standards. At least there is now clarity on what a ‘good test’ might be, but we are still no further in knowing how and when any test should be conducted, nor understanding the limitations and how best to implement a testing strategy.
It is also worth noting that, in the UK, it is currently illegal for any manufacturer to market these tests as ‘home test kits’. Please do not be tempted to source these from any on-line or less than reputable supplier.
Updated information from the government can be found at GOV.UK.
Dr Simon Gillson – Medical Director
Dr Karl Braine – Medical Director