The agency urged current and first-time blood donors to give blood before or immediately after the Canada Day holiday. All blood types are needed, particularly types O and A.
"Right now, we're seeing lower inventory and probably the lowest inventory that we've seen at this time of year compared to the last five years," said Kristina Guénette, director of communications for Canadian Blood Services in Ottawa.
"It's a real patriotic thing to do heading into Canada Day, to really be able to help save the life of a fellow Canadian."
Traditionally, demand for blood is steady over the course of the year, but the blood collections dip when large storms lead to cancellations of donor clinics.
In recent months, about 20 per cent of donors have missed their appointments.
"Historically, donors have come and Canadians stepped in and have been able to provide sufficient amount of donations for us to carry on through the summer. What's changed here is this has much happened much earlier on than we typically see it," Guénette said.
The blood agency has been playing catch-up recently and the concern is heightened as people head into a long weekend where many people are taking four days off, she said.
Platelets — the smallest blood cells that work to prevent bleeding — expire in five days, and Canadian Blood Services hopes donations will cover the longer holiday and build the inventory up to a healthy level.
Canadian Blood Services is responsible for the blood system in all parts of Canada except Quebec, which is served by Héma-Québec.