Give Blood England and Wales

What are false alarms in our tests?

Every day we test thousands of blood donations for infections that can be transmitted via blood. Occasionally, these automated, routine-screening tests can give false alarms (known as reactions). Please be reassured, these false reactions do not have a bearing on your health or the safety of your blood donation.

We hope that this will answer any questions you might have should this happen to you.

Why do false reactions happen?

False reactions occur with all laboratory tests, and a small proportion of blood donations will 'react' no matter which test we use. When this occurs we have set procedures which we must follow.

False reactions are often temporary findings and may occur following:

• A recent cold or 'flu', which can cause antibodies to develop that react with the testing chemicals
• A change to a new manufacturer or a new batch of tests

How can we be sure that the reactions are false?

When we see a reaction in our tests we carry out additional, more detailed, testing on the same sample to clarify the findings. If these tests are negative we can be confident that the reactions are false and are due to technical problems only

What do we do when we see a false reaction?

False reactions have no implications for your health or the safety of the blood. However, our regulations will not allow us to send blood to hospitals unless the initial screening tests are negative, even when we obtain negative results in our additional tests.

The regulations also insist that we must repeat the tests after allowing sufficient time (usually a few months) for the reaction to disappear. To carry out the repeat tests and to avoid wasting blood, we will arrange to take a small blood sample, rather than a full donation, when you next attend. We will then inform you of the test results as soon as possible.

Thank you very much for reading this. We hope you have found it useful and that it has explained a relatively common occurrence sufficiently for you to be reassured should it happen to you.

If you need any more information or advice after reading this, ring our donor helpline on 0300 123 23 23. Our donor helpline is open for general enquiries 24 hours a day, every day of the year. If you have a non-urgent medical enquiry, please try to contact us between 9.00am and 5.00pm Monday to Friday.

False Alarms In Our Tests (PDF, 85K)

False Alarms In Our Tests Welsh (PDF, 61K)