Canada's blood supply is so low that it may start to run dry in a matter of days.

"We are in a critical situation," says Mark Donnison, Canadian Blood Services vice-president of donor relations.

The inventory is at its lowest since 2008, he says.

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"Without the involvement of Canadians, we may have a difficulty meeting patient needs in a few days," Donnison says.

Typically, Canadian Blood Services collects 17,000 donations each week. It needs an additional 7,500 donations in the next week to replenish the supply.

Without those donations, patients with "elective or routine treatments" may be affected, Donnison says. "Hospitals would be facing some challenging decisions about how to triage the treatments."

Right now, there are three days worth of inventory of the major blood groups on hand. The ideal level of inventory is from five to eight days.

While there are many loyal donors – "without them, there would be no blood system in the country, essentially," Donnison says – Canadian Blood Services has seen a decline in the number of people who are walking into donation clinics and a rise in the number of people who aren't able to make their appointments.

"We know that people are really busy, and what we're finding is that at times when blood donations are not top of mind it just kind of drops down the list of priorities," Donnison says.

Only 3.7 per cent of potential donors in Canada give blood.

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Boosting that number is a challenge given how much is involved in giving blood compared with donating to other causes.

"It's a really high-involvement, high-engagement type ask. You have to go to a clinic, we ask a series of questions. You're getting a needle. It takes about an hour. It's more than what a lot of other charitable organizations are really asking for now. With smartphones, people are texting a monetary donation," Donnison says.

Canadian Blood Services is doing more on the "technology front" to stay relevant in the eyes of Canadians, Donnison says.

Earlier this year, the organization launched a mobile app, called GiveBlood, that helps people find clinics and schedule appointments.

A new website that will be more user-friendly is also in the works, Donnison says.

For now, the crucial challenge is getting Canadians through the doors of clinics to donate.

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"Right now, what we're talking about is building awareness about the need for blood," Donnison says. "We need people to come out to donate now."