Ask the Express doctor

Dr Rosemary Leonard ANSWERS YOUR CORONAVIRUS QUESTIONS

Q

I THINK I could have had coronavirus in March when I was unwell for a few days with really aching muscles, a slight fever and felt very tired. I’d really like to know if I’m immune or not, and have seen adverts for private tests. If they say they are CE marked, does that mean the results will be accurate?

A

A “CE” mark means the item conforms to European standards in terms of safety. It means that the test should not spill any nasty chemicals on to your skin, for example. But sadly it says nothing about the test’s accuracy.

There are two types of test for Covid-19.The first is a PCR (Polymerase chain reaction) test, which is done via a swab, when you have symptoms, and can detect whether you have virus particles in your nose or throat.

The second is a simple blood test, pictured below. During and just after the infection, your immune system produces antibodies to the virus, and detecting these, via a blood sample, can show if you have had the infection and are immune. The accuracy of these tests is based on both their sensitivity, which shows how often it correctly measures a true positive result, and its specificity, which is how often it measures a true negative result.

If it has a low sensitivity, then the result could tell you falsely you have no antibodies, when in fact you do, while a low specificity will show you have antibodies, when you don’t. Ideally both these levels should be 99 per cent, and unfortunately it has proved very difficult to produce a test that is good enough (which is why a lot have been thrown away).

I wouldn’t spend any money just yet on a private test, as it’s highly unlikely it is accurate enough to be useful.

If you have a health question for Dr Leonard, write to her in confidence at the Daily Express, One Canada Square, CanaryWharf, London E14 5AP, or email yourhealth@express.co. uk. Dr Leonard regrets she cannot enter into personal correspondence or reply to everyone.