What Happens to Donated Blood?

Blood component therapy

The blood as it exists naturally in our body is called ‘whole blood’, it still consists of several parts (see blood components).

In a normal donation a small amount of this blood, 350-450 ml depending on gender and weight, is collected in a sterile container though a needle punctuating a vein in the donor’s arm.

Every component of natural whole blood serves a different purpose. When receiving blood transfusion however patients most of the time are in need of just one replacement as a certain part of their system failed.

With centrifuges, chemicals and other mechanisms the components of donated blood are separated. That method is called blood component therapy and the standard procedure today.

What are the benefits?

    1. If a patient for example needs red blood cells as he or she is suffering from anemia all the other parts of blood are redundant. The only effect they have is a negative one – the anti gene systems of the patient will realize foreign cells and try to get rid of them. This is exhausting and contra productive for the treatment. So to minimize these immune reactions only the required part of blood is given per transfusion.
    2. With the separation of components within eight hours after donating even storage problems can be avoided – clotting to name one. Furthermore the different parts can be preservedfor different amount of time, if left mixed the ‘shortest’ one would determine the date of expire for the whole unit. RBCs can be stored up to 42 days in a refrigerator, when you freeze them up to 10 years. Platelets however only 5 days at room temperature. Plasma is frozen and can be kept for one year. WBCs aren’t transfused as the defense system is very individual and can’t be transferred from one person to              another. Therefore they aren’t stored either (some exceptions exist but won’t be discussed here).
    3. Up to three persons in need of a blood component can benefit from one unit of whole blood as RBC, Plasma and Platelets are available seperately.
    4. Blood groups exist because of the antibody system on RBCs and in the plasma. For that reason someone with Group A can’t receive a donation from a person with Group B – Group A RBCs would clot with antibodies in Group Bs plasma and vice versa. By separating blood components Group AB+ is a universal Plasma donor (no antibodies in it at all) and Group 0- is a universal RBC donor as they don’t have the protein complexes on their surface.
    5. Not only for transfusion blood components can be used. Some drugs like blood derivatives are made from Plasma.


Blood is likely to contain infectious agents if someone is suffering from a transmittable disease. To prevent the spread of for example HIV, Hepatitis and Syphilis donated blood is screened for the infectious agents. That makes transfusion safe.

Transfusing the wrong blood group can cause huge complications including death. It is very important to confirm matching groups with a simple test – mixing samples of both, patient’s and donor’s blood. With that simple procedure even compatibility concerning anti bodies can be confirmed.

See this depiction for more details and a great chart about the whole process donated blood goes through.


This extraordinary procedure gives parts of the donated unit back to the donor after extracting the needed components. As RBCs need the longest to be reproduced mostly they are transfused back. With that ‘trick’ one can donate plasma and platelets more frequently.

Here you find more information on different types of donation.

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