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Blood Facts

Blood contains four main components:

  • Red Cells - that help carry oxygen to tissues
  • White Cells - that help the body fight disease and infection
  • Platelets - that help prevent bleeding
  • Plasma - that carries proteins and other clotting factors.

There are four major blood types: "O", "A", "B", and "AB". Also, a certain substance, the "Rh- factor, is either present on the red cells or absent.

Approximately 85% of the population has "Rh" factor on their red cells. These people are categorized as "Rh" positive. About 15% of the population lack the "Rh" factor making them "Rh" negative. The blood type breakdown in the United States is as follows:


Blood Type Number of People % of Population
O pos 1 in 3 37.4%
O neg 1 in 15 6.6%
A pos 1 in 3 35.7%
A neg 1 in 16 6.3%
B pos 1 in 12 8.5%
B neg 1 in 67 1.5%
AB pos 1 in 29 3.4%
AB neg 1 in 167 0.6%


The rarest type of blood is the type that is not available when a patient needs it.

It takes 24 to 72 hours to type and test blood after a donation and BEFORE it can be used for patient.

In a crisis, the blood that saves lives is the blood that was donated BEFORE the crisis!

How Much Blood Does a Person Have?

  • A unit of blood is equal to one pint or two cups.
  • For every 25 lbs. of body weight, you have two pints.
  • A person weighing 125 lbs. has 10 pints of blood in circulation.
  • A person weighing 150 lbs. has 12 pints of blood.


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