How do coronavirus home antibody tests work, and how do I get one?

A coronavirus antibody test kit has been approved by Public Health England, The Telegraph has learned, in a breakthrough that could be key to easing the UK’s lockdown restrictions.

What is an antibody test?

An antibody test can 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 to it. 

The coronavirus swab test that the Government currently uses can only tell whether a person has the virus, not if they have had it and recovered. These swab tests also take much longer to get a result.

The antibody test is also known as a “serological test”.

The Telegraph understands that the Department of Health is in negotiations with Swiss healthcare company Roche to buy millions of its coronavirus antibody test kits.

The accuracy of the test was given approval by experts at PHE’s Porton Down facility. Then, on May 13, Roche said it stood ready to provide hundreds of thousands of laboratory-based tests to the NHS each week.

The Elecsys laboratory-based test requires a blood sample to be taken by a health professional. Blood serums are obtained, to which reagents are added, and then examined in machines known as cobas e analysers, already widely installed in NHS labs across the country.

The development of an accurate antibody test is seen as key to helping Britain get back to work.

Scientists believe people who produce antibodies after having coronavirus may develop immunity to catching the virus again, making them safe to return to work.

The Government had previously hoped to roll out millions of antibody tests, but supplies from China failed to pass sensitivity and specificity tests. 

Ministers will attempt to recoup taxpayers’ money spent on the fingerprick tests after an Oxford University trial found they returned inaccurate results.

That failure was a significant setback because it had been hoped the antibody tests would show who had already built up immunity, therefore offering a swifter route out of lockdown.

In April, however, Professor Karol Sikora, a private oncologist and Dean of Medicine at the University of Buckingham, validated a test kit using samples from staff at his clinics, which were then verified by a private lab.

Around six per cent of staff were found to have had the virus but, crucially, under-40s who had tested positive came back negative, suggesting the test may not be useful for the wider population. 

Siemens Healthineers, a German diagnostics and medical imaging firm, also announced on April 23 that it was producing an antibody blood test to identify past coronavirus infections.

The blood tests were expected to be available to large labs by late May, the company said, adding that it would be able to provide more than 25 million tests per month from June thanks to an upgrade to its manufacturing site in Massachusetts.

Another antibody test being pioneered by Oxford University could be available by the end of May, according to Professor John Newton, the UK’s national testing co-ordinator.

What is an antigen test?

An antigen test detects the presence (or absence) of an antigen, not antibodies. An antigen is a structure within a virus that triggers the immune system’s response to fight off the infection. It can be detected in blood before antibodies are made.

An antigen test is effective because it can take a few days for the immune system to build enough antibodies to be detected in a test, however, antigens can be detected almost immediately after infection. So, in theory, the test can tell much sooner whether someone has the virus.

Antigen tests are used to diagnose HIV, malaria and flu.