A false positive test is when the test result shows positive but the person is really negative. This can happen with antibody tests when the test picks up antibodies for other infectious agents.
Approximately 1.5% (15 out of every 1000) antibody tests are a false positive. The fourth generation tests have a much lower chance of a false positive.
This means that a small percentage of people who test positive on a rapid test (where the results are given within an hour) may turn out to be HIV negative.
A second blood sample will be tested in a lab to look for this.
If your blood test was originally performed in a laboratory, a positive result would have already been confirmed before giving you this result.
All positive laboratory tests in the UK are routinely confirmed using a second type of test called western blot that is 100% accurate.