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Frequently Asked Questions
"False-Reactive" Screening Test Results

  1. What is meant by a "false-reactive" (or "false-positive") test result?
  2. Why did I test "false-reactive"?
  3. Do I need to go to my doctor for repeat testing?
  4. Do my partner, children, or friends need to worry?
  5. What do the tests Canadian Blood Services conducts look for?
  6. What method does Canadian Blood Services use to test blood?
  7. Why doesn’t Canadian Blood Services just skip the screening test and test all blood straightaway with tests to find the markers that are only present with infection? Wouldn’t this avoid the possibility of a "false-reactive" test?
  8. I went and had follow-up testing done by my doctor and my test result was "non-reactive" (or "negative"). Why can’t I continue to donate?
  9. Is the current policy towards permanent deferral of "false-reactive" donors ever likely to change?
  10. If I have had a "false-reactive" screening test, can I still donate blood for my own use at the time of surgery (autologous blood donation)?
  11. Who do I contact for further Information from Canadian Blood Services?

1. What is meant by a "false-reactive" (or "false-positive") test result?

A "false-reactive" (or "false-positive") test result means that the initial screening test was "reactive" but a more precise follow-up test was negative.

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2. Why did I test "false-reactive"?

Almost all false-reactive test results occur because of interference with the test and are not due to infection.

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3. 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 give you personal medical advice.

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4. Do my partner, children, or friends need to worry?

No. Receiving a false-reactive test result can be worrisome and upsetting. But tests that are false-reactive really mean that infection is not present in the blood. So you would not have exposed your partner, children and friends to any tested infection or disease. If you have any additional concerns you should speak to your physician who can give you medical advice.

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5. What do the tests Canadian Blood Services conducts look for?

Every donation given at a Canadian Blood Services clinic is tested for the presence of infection due to hepatitis viruses B and C, the AIDS virus (HIV), syphilis and another uncommon virus called HTLV (Human T-Lymphotropic Virus). HTLV is not the virus that causes AIDS.

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6. What method does Canadian Blood Services use to test blood?

Canadian Blood Services uses a "two stage" testing method. This "state of the art" method of testing the blood for the presence of infection is used by laboratories throughout the world. In the first stage, a sensitive "screening" test is used to look for the possible presence of infection. If the screening test shows no reaction, and then 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" screening test is due to infection in the blood or to interference with the test. This further testing identifies markers in the blood that are only found when an infection is present.

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7. Why doesn’t Canadian Blood Services just skip the screening test and test all blood straightaway with tests to find the markers that are only present with infection? Wouldn’t this avoid the possibility of a "false-reactive" test?

The "two stage method" is the best method of screening for infections in the blood. The screening test is very sensitive and can be completed quickly to allow the blood to be used for transfusion. The screening test almost always correctly identifies an infected blood donation. Reactions may also occur in the absence of infection because the screening test is so sensitive. Whenever a reaction occurs in the screening test, the blood is not used for transfusion and further testing is done to determine whether an infection is present. This additional testing takes more time.

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8. I went and had follow-up testing done by my doctor and my test result was "non-reactive" (or "negative"). Why can’t I continue to donate?

Current regulations say that a donor can no longer donate blood for others after having a "reactive" test result, even if further testing by their own doctor is "negative". The mission of Canadian Blood Services is to ensure a safe, secure blood supply for all Canadians. The highest standard of safety is achieved by accepting only those donors who have always tested "negative" for infections. Therefore, as a precautionary safety measure, donors with "reactive" test results are permanently deferred from blood donation.

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9. Is the current policy towards permanent deferral of "false-reactive" donors ever likely to change?

Canadian Blood Services is reviewing the policy of deferring donors with false-reactive test results with the intention of recommending to Health Canada that these donors be allowed to start donating again. In order to do this; additional tests would be required. Health Canada must approve this new procedure which is a long process, requiring extensive evaluation by Health Canada.

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10. If I have had a "false-reactive" screening test, can I still donate blood for my own use at the time of surgery (autologous blood donation)?

Yes. With the recommendation of your own doctor, and the approval of the physician in charge of the hospital blood bank, you will be able to donate blood for your own use prior to certain elective surgical procedures. You will also have to meet the donor eligibility requirements for the Autologous Blood Donation Program.

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11. Who do I contact for further Information from Canadian Blood Services?

If you have questions please e-mail us at feedback@blood.ca.


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