The New York Blood Center says its supply of O-negative blood — the kind that can be used to treat any patient — is critically low.

The center, which distributes blood to hospitals, has declared its second “blood emergency” of 2024 and says donors are desperately needed.

“Across all blood types, we like to have a seven-day supply on the shelf at all times,” said Chelsey Smith, a spokesperson for the New York Blood Center. “When our inventory drops below a seven-day supply, that’s cause for concern” and typically triggers a blood emergency.

O-negative is the most commonly used blood type in emergency rooms because it’s compatible with all other blood types, Smith said. She added that, as of Friday, the center was down to a two-day supply of both O-negative and B-negative blood and had a “critical shortage of platelets.”

The Blood Center says it needs to collect about 2,000 individual donations of blood a day to supply area hospitals. But dipping below the ideal inventory of a seven-day supply doesn’t necessarily mean patients in need of transfusions won’t get them. For one thing, blood emergency declarations — which may be made a few times in any given year — are usually effective in getting more people to donate quickly, Smith said.