Canadian Blood Services is calling on the public to roll up their sleeves to help reduce a nationwide blood shortage that's reached what it calls a critical level.

The organization currently has between 12,000 and 14,000 units of blood on hand; the country typically requires a minimum of 20,000 units at any given time.

"It is critical right now," said Hailu Mulatu, a regional manager with Canadian Blood Services. "We're trying everything we can to ensure that we can meet patients' demands over the summer."

While Saturday marks the last day of National Blood Donor Week, Mulatu says Canadian Blood Services is extending its appeal for donations.

The goal is to bag 50,000 units of blood by the end of June, a target that will take a major surge to reach.

Increasing the blood supply is, without exaggeration, a matter of life and death for thousands of patients around the country, Mulatu says.

Victims of a bad car crash can need up to 50 units, while leukemia patients can require up to 80 units every week, the organization estimates.

Life-saving blood

Eleven-year-old Aaryan Dinh-Ali also relies on massive amounts of blood on an ongoing basis. 18 months ago, he was diagnosed with aplastic anemia, a rare bone marrow disease which caused brain bleeding and reduced his blood count to dangerous levels.

In his treatment and recovery, Dinh-Ali has received around 100 blood transfusions.

"Aaryan has countless strangers' blood running through his system so he can function on a normal basis and be where he is today," his mother Jenny Dinh said.

"If it wasn't for those transfusions, Aaryan may not have survived and come home with us."

Hailu Mulatu of Canadian Blood Services warns that hospitals may start to cancel elective surgeries if the shortage continues. (SickKids)

Why the shortage?

Mulatu believes this year's shortage has been caused in part by bad spring weather, which forced the closure of some Canadian Blood Services clinics over the last few months.

With those clinics now back open, he's hoping Canadians recognize how valuable their donations are for patients battling disease and recovering from accidents. Mulatu also notes that hospitals may take other steps to preserve the dwindling blood supply.

"With a low blood inventory, what may happen is that hospitals may be asked to reduce the amount of blood that they use, which may delay elective surgeries," he said.

Geoffrey Brown has donated blood more than a hundred times..

"For a first-timer, it might be a little intimidating but the people there are all very kind and appreciative of what you're doing," he said. "It's always a degree of satisfaction knowing what you're doing can assist a number of different people with whatever health problems they are undergoing."

Jenny Dinh-Ali says her son's ordeal also opened her eyes to the staggering importance of blood donations. Seeing the public inventory so low is even more painful after her experience over the past year-and-a-half.

"It hurts because not only is it our child who's in need of blood, but being in Sick Kids Hospital for a month straight and seeing the children in there … everybody needs to donate," she said.