Analysis of Covid-19 testing
"Tests are good for satisfying people’s curiosity, but no more. We just don’t know enough about what it takes to make someone immune to Covid-19 to accurately test people."
The above comment from Dr Simon Clarke, Associate Professor in Cellular Microbiology, University of Reading, is just one of many conflicting statements on coronavirus issues made by various experts worldwide, but probably nearer the truth than most. The Spanish government recently paid for 640,000 antigen coronavirus tests. After testing, they were found to be faulty. A replacement order was also proven to be sub-standard. This was by no means an isolated case. The UK government purchased two million home test kits. These were also found to be inaccurate. Half a million of the tests are now gathering dust in storage. Another 1.5 million bought at a similar price from other sources have also gone unused. The obvious question here is, why were these kits not tested prior to placing orders? Maybe too simple logic for politicians and scientific experts?
So what tests are available and how accurate are they? Basically, there are three types of tests on the market:
Antigen/diagnostic - This swab test, usually taken from inside the nose or mouth, already exists and indicates whether a person is currently infected with the disease. This type takes longer to process as the samples need to be analysed in a lab.
Antibody tests - Designed to detect if a person has had coronavirus before and has since recovered. The test, carried out by a device that pricks your finger for blood, works this out by testing your blood for coronavirus antibodies to see if they have already beaten the virus and gained some immunity. The antibody test needs to be analysed at a laboratory or hospital with the appropriate equipment.
Lastly, widely promoted on the web, are Covid-19 antibody home kits. Sellers claim they give you an instant result, similar to a home pregnancy test indicator. Regulatory Agency (MHRA) has raised concerns that any company selling these at-home test kits, should be avoided. No test of this type is approved by the Agency.
The government free test scheme will be limited to anyone showing signs of having contracted the virus, front line workers, the elderly and most vulnerable. But since lockdown regulations have eased, various private hospitals and clinics have started to offer antibody tests at fees varying from €45 €145. As previously reported in this newspaper, Carlos Ruis, President of the Private Health Alliance, says the cost of tests to the industry is around €8, plus IVA and transport and that the price for private testing should be around €30.
Regardless of availability and costs, in the real world, researchers still don’t know what the false positive rate is, but clinical sensitivity of RT-PCR tests ranges from 66% to 80%. That means nearly one in three infected people who are tested will receive false negative results. The World Health Organisation warned against making assumptions about a person’s immunity to Covid-19 based on antibody testing. A positive result should not yet be interpreted as a stamp of immunity. Prof Gino Martini, Royal Pharmaceutical Society Chief Scientific Officer, said: “Any antibody test at present can only provide a partial picture. The real issue is that no-one knows the level of immunity that is conferred by having antibodies to coronavirus.
Final comment from Prof Adam Finn, Professor of Paediatrics, University of Bristol, "If a person takes a test and gets a false positive, they may assume they have been exposed and that they have immunity when they do not. They may expose themselves to risks when they shouldn’t. If a person gets a false negative result, they may think they are at risk of infection and pose a risk to others when they really are immune and perhaps the risks are less. But most important of all, until we know how strong and long-lasting immunity is after infection, it is hard to know what to do about the results of these tests, even if the tests are reliable."
Confused? So am I.
The views and opinions expressed in this article are those of the author and do not necessarily reflect the official policy or position of the Costa Blanca News group
Benny Davis investigates the world web reporting on coronavirus testing