By: Delthia Ricks / delthia.ricks@newsday.com

An emergency appeal has been issued to potential blood donors from throughout Long Island and New York City in the wake of Thursday's powerful snowstorm, which caused 1,600 donors to cancel appointments, forcing already tight supplies of several blood types to reach critically low levels.

Supplies of O-negative blood - the universal donor - are among the units in short supply, according to the New York Blood Center in Manhattan, which provides blood and blood products to Long Island's 25 hospitals and serves 20 million people in the greater New York City area.

O-negative blood, usually maintained at a three- to five-day inventory, has plunged below a two-day supply, blood center officials say.

Equally worrisome, a range of blood products, including platelets, are also in short supply. Platelets are sticky, disc-shaped cells that aid in clotting. Rob Purvis, vice president of the New York Blood Center, said the mass cancellations of appointments due to heavy snow seriously amplified a blood-supply shortage that has been looming all winter.

"People have been digging out and just couldn't make it," he said of the cancellations.

Over the past six weeks, 8,000 fewer blood units are on shelves due to inclement weather, he said.

"We are able to meet the needs of the hospitals today," Purvis said. "No one is without blood, but supplies are getting low."

Purvis noted the American Red Cross has issued a similar appeal for blood in the wake of dwindling supplies across the country.

"Right now, we are kind of holding our own," said Janet Freedman, nurse-manager of the Blood Donor Center at Nassau University Medical Center in East Meadow, which receives blood from the New York Blood Center and its own collection efforts.

Dr. Andrew Heaton, senior director of transfusion medicine for the North Shore-LIJ Health System in Manhasset, said his hospitals fortuitously started bracing for low supplies in recent days. Anyone interested in donating blood or organizing a blood drive can phone the New York Blood Center at 800-933-2566 or visit its website at nybloodcenter.org.