Over the past 25 years there have been many breakthroughs in blood screening technology that have allowed blood collection agencies to modify and relax regulations surrounding other categorically high-risk donor groups.

No one challenges the fact that people who are aware that they are HIV-positive should refrain from donating blood. Throughout the 80’s, most people including MSM believed that this draconian policy made sense in light of the devastating nature of HIV infection. The then limited epidemiological data and knowledge of how HIV is transmitted and the relatively crude tools available to detect the virus in blood seemed to provide justification to the policy.

Since 1985, policy makers have been most worried about the window of time between the point of infection with HIV and the point at which screening tests can detect an infection in a blood donation. The early laboratory tests that screened blood for HIV looked for antibodies to the virus, which take several weeks, and in some individuals several months to develop. Blood policymakers worried that during this window, HIV-tainted blood might slip through the screening mechanism.

This is where conditions have changed most dramatically. The nucleic acid test (NAT) has become the standard by which all blood donations are screened in Canada. It amplifies and looks for small fragments of HIV RNA in pooled samples from 512 units of donated blood at a time. According to Health Canada it is virtually foolproof and able to detect HIV in pooled blood within 12 days of infection. If the technology is used on individual rather than large pooled samples, NAT can detect HIV within 4 to 5 days, according to testimony before the Food and Drug Administration (FDA) by Michael Busch, MD, with the Blood Centers of the Pacific. As a result, policies involving non-MSM donors have changed to reflect the safer blood screening process.

Current duplicate testing using NAT and serologic methods allow detection of HIV-infected donors between 3 and 21 days after exposure.  Beyond this window period, there is no valid scientific reason to differentiate between individuals infected a few months or many years previously. 

The Donor Selection Questionnaire was developed in recognition of the importance of stimulating recall of recent events to maximize the identification of donors at risk for incident, that is, recent, infections.  From the perspective of eliciting an appropriate risk history for exposure to HIV and other sexually transmitted infections, the critical period is the three weeks immediately preceding donation since false negative NAT and serology reflect these window-period infections, and the length of these window periods provide the scientific basis for the deferral periods imposed for at risk sexual behaviors.