‘BE WARY OF DODGY ANTIBODY TESTS’

The government has an antibody test, but lots of shops are selling their own versions – Dr C says to hold on to your cash

You might have seen shops offering at-home antibody tests, to detect if a person has had coronavirus before and has since recovered. They’re pinprick tests that you then send off to a lab to get your results. Thousands of people have bought them. But Public Health England has approved a test that will initially be made available in hospitals and care homes, and that’s the only one I would trust.

A finger prick test is fine as a method – it’s how we test for HIV – but the difference is the accuracy. The government-backed test is 99.8 per cent accurate, which I would expect, and that is the same figure for tests like the HIV one. Anything less than that, I would be suspicious of, and the on-the-shelf one I have seen is 97.5 per cent.

If you’re tempted to buy one, the key is to look at the accuracy number, and if it’s any lower than 99.8 per cent,

I would avoid it – especially as you’re paying for it.

Those two numbers, 99.8 and 97.5, may sound close, but that tiny difference is crucial. If a test is 97.5 per cent accurate, that means that a little over two in every 100 tests will falsely reassure somebody that they have antibodies.

If a million people took the test, that means more than 20,000 people could be falsely reassured they have antibodies when they don’t – and that’s very important with a pandemic that could have a second spike, because they could go out and unwittingly spread the virus. Keep your cash and wait for the government one.