False reactive test results

What if I have a ‘false reactive’ test result?

Every donation given to Canadian Blood Services is tested for infectious diseases caused by the hepatitis viruses B and C, HIV, syphilis and another uncommon virus called HTLV (Human T-Lymphotropic Virus). 

A false reactive (or "false-positive") test result means your initial screening test was reactive—in other words, suggested the presence of something that would prevent you from donating blood—and a more precise follow-up test was negative. Almost all false reactive results occur because of interference with a test and are not necessarily due to testing positive for an infection. 


How does Canadian Blood Services test blood?

We follow a two-stage testing method that is used in laboratories worldwide. In the first stage, a sensitive screening test looks for the possible presence of infection. If the screening test shows no reaction, the blood is considered free of infection and no further testing is done. However, if the screening test is reactive, further testing is done to sort out whether the reactive result was due to an infection in the blood or interference with the test. The second test identifies markers in the blood that are found only when infection is present.

Do I need to go to my doctor for repeat testing?

Yes. Repeat testing should be discussed with your doctor because he/she is in the best position to offer you personal medical advice.

Do my partner, children, or friends need to worry if I've had a false reactive result?

No. A false-reactive test result can be surprising and upsetting, but it also means that there is no infection in your blood, meaning your partner, children and friends would not have been exposed to any tested-for infection or disease. Talk to your physician if you have any concerns: he or she will be happy to give you medical advice.

Why not skip the screening tests and test all blood right away for infection markers to avoid false-reactive results?

The two-stage method is the best method of screening for infections in the blood. The screening test, while very sensitive, can be completed quickly to identify blood that can be used for transfusion. The additional testing takes more time. So, it is used only for donated blood that produces reactive screening results, to determine if those results are false or true.

How do I participate in the donor re-entry program for false reactive screening results?

Eligible donors will be invited, by letter, to participate in Canadian Blood Services’ donor re-entry program. It is important that the mailing address you have provided is up to date to ensure that you receive this letter. The letters are typically sent after a six-month period following a “false positive”.

Many, but not all donors with “false positive” test results are able to participate. Currently, donors who test false positive for HIV, Hepatitis C, Syphilis and Human T-cell lymphotropic virus I and II (HTLV) are eligible, as alternative testing is available. Donors who have received a Hepatitis B vaccine within two weeks of testing and test false positive for Hepatitis B surface antigen (HBsAg) will also be invited to the re-entry program.

As new testing assays become available, more donors with false positive results may be able to participate in the re-entry program.

There are many reasons why a “false positive” result happens. It could be an issue with the test, how the blood might have been collected, and sometimes it is related to the donor. More common temporary causes are changes in the donor’s blood which may occur when they are recovering from an infection or illness or have recently had vaccinations. There are even some food items and herbal supplements that can interfere with testing; however, this is less likely. Our body is constantly adapting to our environment and some of these normal changes can interfere with testing. Despite ongoing advancements in screening tests, none are perfect, and a “false positive” result is a common occurrence during eligibility testing. You will become eligible to participate in the donor re-entry program six-months after a “false positive” test.

For donors who are invited to the re-entry program, the date of eligibility will be noted on the letter informing them of the “false positive” test result.

After six months, we ask that donors who have received a “false positive” test result call 1 888 2 DONATE (1-888-236-6283) to speak with one of our health professionals about getting re-tested, as part of the donor re-entry program. We will confirm a donation centre location and appointment time over the phone.

When donors attend their re-testing appointment, they are asked to bring the letter that was sent from Canadian Blood Services. At this appointment, only a small amount of blood for testing will be collected. The sample will then be tested, and a follow-up letter will be sent to the donor to advise them of their results. If all results are non-reactive, you may once again be able to donate.

Follow-up testing by my doctor was non-reactive. Can I continue to donate?

Our approved re-entry process includes being retested by our health professionals a minimum of six months after your last donation. If all your test results are non-reactive or ‘negative’ at that time, you will be able to donate again. This is our official practice to become a part of the re-entry program.

What happens if additional tests of my blood come back positive?

If a false positive reactive test occurs a second time, you will no longer be eligible to donate blood. Being deferred indefinitely does not mean you cannot support our organization anymore. There are many ways to give and all of them are of vital important to our mission to save lives. Please call us at 1 888 2 DONATE (1 888 236-6283) to learn about other ways to donate.

If I had a false-reactive screening test, can I be a OneMatch stem cell donor?

You may be eligible to register in the OneMatch program as a potential stem cell donor provided that you meet all other eligibility criteria.