Ron Vezina explained the recall was ordered Friday after the agency learned that some of its nurses or other staff were not asking all the oral questions required during the donor screening process.
"The oral questions tend be ones about travel risk or sexual practices or other things that might put donors at risk," he said.
But he stressed that doesn't mean any of the blood products were tainted.
"We believe that the risk in this case is remote, the next thing to not-at-all," he said.
"Every unit of blood goes through infectious disease testing and cannot be released to a hospital until it tests negative. Anything that went to a hospital already tested clean.
"This is really just about us saying we're very committed to our standards, and when our standards are not met we bring the product back."
The agency also closed its doors to donors Friday so it could hold a staff meeting and reinforce the need to follow all procedures to the letter.
"One or more employees that may not have been doing that correctly," he said, adding the lapses tended to be with high-frequency donors.
Vezina didn't want to speculate on why staff weren't asking all the questions, but insisted it was not a matter of a bad process, simply a question of the process not being followed.
"We're quite convinced that the training is pretty black and white about the importance of going through every step," he said.
"Some of that screening might become really repetitive to folks that do it a lot or see donors time and time again, but (the staff meeting) was to reinforce that the rules and regulations are there for specific reasons."
The recall dates back to Oct. 2, 2011. That could mean there is still frozen plasma, which can be held up to 12 months, that might be recalled, as well as red cells, which have a shelf life of 42 days.
Platelets must be used within five days.
Vezina said it's unknown how much blood product that would fall within that year callback ended up being used on patients, but allowed there would likely only be a small percentage that would still be in inventory.
He said patients who were given blood products within that span of a year would not be tracked down.
"Because this is such a low risk and because there's national standards on this, there's only a remote risk to patients and it doesn't warrant notifying those patients because the risk is so low."
Dr. Ted Alport, medical director for Canadian Blood Services in Saskatchewan, could not be reached for comment but said in a news release the matter was being taken seriously.
"We apologize for any donor inconvenience and encourage donors to continue their generous support," the release said.
"We are equally committed to openness and transparency and take our accountability to Canadians seriously. This public statement is a testament to that commitment."
-- By Gwen Dambrofsky in Edmonton