False positive results

A “false positive” result occurs when the screening test gives a positive or reactive result but the confirmation test reverses that finding with a negative or undetermined result. 

A two-stage analysis process

Héma-Québec uses a two-stage analysis process.

Screening test

This involves subjecting the blood to a highly sensitive test to detect signs of infection. If there is no reaction, we conclude that there is no infection and the analysis ends there.

Confirmation test

When a reaction does occur, the blood is subjected to a second, more advanced test to determine if there truly is an infection or if it was a false reaction.

What causes a “false positive” result?

Despite improvements in screening tests, none are perfect. Occasionally, proteins or chemical agents in the blood cause a first positive result, even when there is no infection.

Staff in charge of blood services and at Health Canada’s Health Products & Food Branch are well aware of the possibility of “false positive” results and explain this phenomenon by the high degree of sensitivity of the tests used. At Héma-Québec, five to ten “false” reactions are recorded each week from among the thousands of blood donations analyzed. The sensitivity of the tests ensures their reliability.

The sensitivity of the screening tests can be compared to a smoke detector alarm that suddenly goes off when the device detects heat or smoke. The detector’s sensor sets off the alarm even when the heat or smoke is not from a real fire. The sound alerts us to quickly check if the fire is real or if it is a false alarm.

Should I worry if I have a “false positive” result?

No, a “false positive” result or “false alarm” is a common occurrence during eligibility testing. It does not mean that you have an infection, and there is no risk to your loved ones (partner, children, etc.).

How can I be sure that this is my blood?

We can guarantee this because all the usual verifications were carried out from when you donated the blood to when the result was sent to you. All the donation steps (from blood collection to delivery to hospitals) are strictly regulated and are the subject of regular inspections by Health Canada.

Should I talk to a doctor if I have a “false positive” result?

Only if you wish to. The result of the confirmation test shows that you were not infected.

If my blood is subjected to other tests and the results are negative, can I start giving again?

Call us at 514 832-5000, ext. 5477 or toll-free at 1 888 666-HEMA (4362), ext. 5477, and specify that you are calling regarding the donor re-entry program. We will answer your questions.