This article about COVID-19 testing covers:
- The different types of tests available
- The accuracy of the tests
- Some of the other problems with testing
- The testing process currently available
- Public Health England warning about certain test kits
- CQC guidance about testing
We’ve been constantly monitoring the different tests that are becoming available to support identifying and managing COVID-19 cases. Although are still many unknowns about the accuracy of some of the tests, we’re pleased to be able to share our current thinking. We’ll continue to keep you updated in the coming weeks too.
The different types of test
There are two different tests to identify if someone has, or has had, COVID-19. The first, an antigen test, is designed to show if anyone has the virus at the moment the test is taken. The second, an antibody test, is intended to find the antibodies created during or after the body fights off the virus.
Both types of test are currently available privately, however, both have a few potential problems and we currently suggest conducting research before using the tests.
The antigen PCR (“swab”) test uses the genetic code from the virus to detect any presence of the virus in the body. Many of the tests available have a good ‘limit of detection’, in that they can accurately identify very small amounts of the virus in the body. However, the tests have high levels of ‘false negative’ results.
The antibody test looks for either one (or both) of the two different types of antibodies created by the immune system during and after it fights off the virus. It requires a small blood sample.
Although there has been lots of news coverage recently about an antibody test (made by Roche) being approved by Public Health England, it is likely to be some time before it becomes more widely available. Another test produced by Abbott Laboratories (which we are now using within our COVID-19 Antibody Test service) has also been approved by Public Health England. None of the unapproved tests available currently are particularly accurate.
For either test to be perfect, every positive result would mean you definitely had coronavirus and every negative result would mean you definitely didn’t. Sadly, this isn’t the case with many diagnostic tests and COVID-19 is no exception.
True positive and true negative results
As both types of test for COVID-19 have been developed incredibly quickly and under emergency circumstances, it’s no surprise that many people have questions and concerns about their accuracy.
It’s best to think of the accuracy of the test in two ways; the true positive rate (called ‘sensitivity’) and the true negative rate (called ‘specificity’).
Sadly, although the PCR swab test is good at accurately identifying the presence of the virus (the true positive rate) it has weaknesses in the accuracy of some of the negative results given. Some reports suggest a false-negative rate of up to 30%.
That means that if ten people who are actually infected with coronavirus are swabbed, up to three of them will receive negative results despite having the disease.
Why should a GP consultation be required?
Although COVID-19 tests can be purchased online from many sources, not all the services include advice and support from a named clinician, which we think is a particularly poor standard of care.
If you have any questions about the test, pre-existing conditions, the results and what they may mean, you will not be able to access advice from the test providers. Support is often limited to contacting a generic email address.
Our Regulator, the Care Quality Commission, expect good medical providers to be able to demonstrate that their service is safe, effective, caring, responsive and well-led. We think the only way to achieve that whilst offering tests remotely is to ensure that a responsible clinician has oversight of tests, results and the follow-up process.
If you are considering ordering any test online, we urge you to consider the level of support you can access from a clinician as part of the service, before, during and after the test.
Other problems with testing
There are several other factors that can affect the rates of true positives and negatives that are independent of the accuracy of the test itself:
- The test may be taken too early for the virus to be detected
– patients who have just contracted the virus may have very low levels in their body at the time test is taken. This is why the test can only be taken from 48 hours after symptoms have started. It cannot be used for patients who do not have any symptoms.
- The sample is collected too late – if the sample is collected after the infection is waning, there may not be enough virus in the
body to be detectable by the test. However, the patient may still be
- The sample is contaminated – healthcare workers or lab technicians handling the sample may inadvertently contaminate the sample (commonly via gloves or from other surfaces), triggering a false positive.
- The time between sample collection and processing is too long – the longer a sample is stored before testing, the more it can degrade. Extended storage, transporting time or delays before processing can lead to both false positives or negatives.
- The sample is not collected correctly – the swab must be taken from far back in the throat and nose and often causes a gag or cough
reflex, which is why most healthcare workers are heavily protected whilst obtaining samples. If the sample is not collected properly a false negative may be provided. This is a known weakness in using home testing kits.
Swab testing in more detail
Although the swab test is widely available, we have taken the view that offering the test privately was likely to be taking resources from essential workers and their household members, or from patients in whom testing to confirm their diagnosis would alter their management.
However, the availability of tests is improving and it is likely that we’ll be able to review the situation again in the next week or two.
Public Health England have also issued a warning about certain swab test kits being offered for use in local pharmacies or at home, because they may be highly inaccurate. The warning applies to ‘rapid result’ test kits, which offer results from a swab test within 10 minutes.
If we do commence offering the swab test, we’d recommend that it is only provided to suitable cases. We’re unlikely to recommend it as being suitable for those with only mild symptoms, as the individual will have to self-isolate anyway.
To make sure we’re only testing appropriate cases, we’ll need to screen patients to confirm if they are suitable for the test, which is easily done with a quick conversation with a doctor or via an online assessment tool.
It’s important to note that the test will only show if an individual has the virus on the day the test is taken – if the result is negative the individual may still contract the virus the following week, for example.
How does the swab testing process work?
We wouldn’t wish to suggest anyone pays for the test if it is not going to make any difference to the advice given. If an individual has the symptoms to warrant testing, the guidance about self-isolation will still apply up to the point the result is given, which may well be very close to the end of the required isolation period anyway.
What happens with a negative or positive result?
However, the test does have value in deciding the period of isolation that will be required for household members. If the result is negative, the individual may return to work and household members will not have to self-isolate. If the test result is positive, all household members will need to isolate for 14 days.
It’s not currently possible to provide a stock of test kits for employers or patients to hold ready for future use, because the tests are provided within accredited quality systems and all positive results are automatically referred to Public Health England (because the virus is a notifiable disease). Each kit is provided on a named basis, under the guidance of a responsible clinician.
How long do results usually take?
The testing process is usually likely to take around three, possibly four, days to complete from the time the screening process is completed.
The government has also advised that they are providing free antigen (swab) testing for everyone in the country over the age of five who has symptoms.
We would advise the government operated service as probably being the most appropriate mechanism for employers, as it is free at the point of use.
However, private testing services may still be appropriate should the service prove inaccessible or unreliable.
What about antibody testing?
Although there is lots of coverage in the news today about a test receiving Public Health England approval, it is not currently widely available. The test we are now using to provide our COVID-19 antibody test service uses a test produced by Abbott Laboratories, which has also received approval from Public Health England and is also highly accurate.
Although we are providing the test, we do not currently have any information about whether having had the virus confers any future immunity or not. However, understanding if you have had the virus or not may still be helpful information for individuals.
We’ve been advised by our Regulator (the CQC) not to provide antibody testing unless the test being used is approved by Public Health England, which are again pleased to confirm is the case.
What about repeat testing?
It may be helpful to retest individuals if they are displaying symptoms of COVID-19 and have previously tested negative. Although there is some speculation about the possibility of reinfection with the virus, there is no guidance currently on retesting after previous confirmed cases. There is little evidence at present to support periodic retesting of individuals otherwise.
We’ll be refining our advice and guidance as we continue to learn more about the virus, particularly about surveillance schedules for any population monitoring and contract tracing, as they’re rapidly developing situations.
How do I request a test?
To discuss anything else to do with COVID-19 testing, please contact us.
Occupational health support
It’s currently incredibly difficult to provide definitive advice about lots of elements of managing COVID-19 risks for employers, because so much about the virus is still unknown.
Please feel free to contact our occupational health team on 02072363334 if there is any further information, assistance or support we can provide.
To learn more about our occupational health services for business, please visit our occupational health pages.