Look Back

Look Back

Despite strict screening procedures and highly effective testing, there is the potential, in rare instances, for an infected unit of blood to be released for transfusion. The potential for this lies in the fact that, as effective as these safety procedures are, they are not perfect.


  • A donor may lie, or simply be unaware of a risk factor.
  • A virus may not be detectable if the infection occurs within the window-period before current tests are able to detect it.


Canadian Blood Services has two processes in place to limit the potential damage of an infected donation.


  • A trace-back begins with a patient who may have a transfusion-related infection. Canadian Blood Services conducts a targeted search to identify which donor(s) gave that person blood.
  • A look-back begins with an infected donor. Canadian Blood Services conducts a targeted search to identify what patients received that donor’s blood.


If Canadian Blood Services discovers that a potentially infected unit of blood has been released for transfusion, either through a trace-back or through receipt of post-donation information from a donor, Canadian Blood Services takes immediate action:


  • Canadian Blood Services begins the look-back procedure
  • If the unit is in inventory, it is destroyed
  • If the unit has been sent to a hospital, it is recalled
  • If the unit has been transfused, Canadian Blood Services notifies the hospital to inform the recipient of the potential risk


In the event that the donor has donated plasma, his/her donation may have been pooled with those of thousands of other donors. In this case:


  • Canadian Blood Services works with the manufacturer to trace the products made from that donation
  • Canadian Blood Services then orchestrates a withdrawal of all affected products from hospitals
  • If any of the affected products were used, Canadian Blood Services advises hospitals to inform recipients of potential risk