The tests performed by Canadian Blood Services are so sensitive that they sometimes produce "false reactive" or "false positive” results. This occurs in a small number of donors when elements in their healthy blood trigger a reaction.

All units that produce initial positive results are subjected to additional, confirmatory testing. If confirmatory testing produces a negative result, the unit is considered a "false reactive" or "false positive". A negative result in confirmatory testing is reassuring news for the healthy donor.

Nevertheless, no unit that initially produces a reactive result is ever transfused. Canadian Blood Services errs on the side of safety. It destroys any blood unit that tests "reactive" or "false positive" and maintains records so that these individuals are not accepted for blood donation in the future.

False Reactive Frequently Asked Questions