PALO ALTO (CBS SF) — Bay Area residents are being asked to donate blood as soon possible due to a severe shortage, Stanford Blood Center officials said Friday.

Supplies of blood types O-Negative, AB-Negative and B-Negative have been depleted by recent patient usage, including a liver transplant surgery, pediatric heart surgery and pediatric leukemia treatments.

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A seasonal drop in blood donations is also a factor, according to the Stanford Blood Center.

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“We’ve put the call out to our current donors, and now we’re appealing to others in the community for their help,” Stanford Blood Center spokesperson Loren Magana said in a statement, calling the shortage “critical.”

Donors should be healthy with no symptoms of the cold or flu. The process takes about an hour. Potential donors are being asked to call (888) 723-7831 to make an appointment.

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