Each component serves a unique purpose, said Philip Mohr, professor of microbiology. Red blood cells are the primary cellular components of blood. Plasma is simply the liquid portion of blood. Platelets are involved with clotting.

Test tubes of blood taken at the end of the donation are sent to Philadelphia and go through up to 13 tests to ensure safety, Keeler said. These tests look for diseases such as HIV, hepatitis, syphilis, atypical antibodies and West Nile virus. Ninety-nine percent of samples sent to the testing laboratory are screened within 24 hours and nearly 6.9 million were screened nationwide last year.

The Red Cross has begun Nucleic Acid Testing to identify the presence of HIV and hepatitis C in blood donations, Keeler said. Donors with positive results are notified and have the opportunity to talk with a Red Cross health care professional catches things earlier than ever before possible. It's not perfect, but it's the best test that's out there," said Marianne Spampinato, director of public relations for the Greater Alleghenies region.

While still in Philadelphia, the ABO/Rh type, commonly known as the blood type, is also determined. The Rh factor refers to the presence of a particular antigen in the blood. If present, the blood type is positive; if not, it is negative.

O positive and A positive are the most common blood types, with approximately 35 percent of donors having each type. B negative and AB negative are the rarest, with 2 percent and 1 percent of donors, respectively. Keeler said there is a great need for type O Negative blood, since it is the universal blood type and can be used by anybody. About eight percent of donors have that type of blood.

After the blood is cleared for use, the main units of blood are shipped from Johnstown to as many as 100 hospitals and given to patients with the appropriate blood type. Blood unit needs vary greatly by patient -- hip replacement surgery requires between two and five units, while organ transplants may need up to 200 units.

"We get blood every day, sometimes twice a day," said Gloria Martz of Centre Community Hospital. Martz said the hospital maintains an inventory of blood, organized by type, which the Red Cross keeps stocked.

Blood will decompose much faster if stored at the wrong temperature or not delivered to patients in time, Mohr said.

Red blood cells must be transfused within 42 days unless they are frozen, and platelets remain usable for only five days.