What is blood?

Blood plays many vital roles. From protection against infections to the transport of oxygen and nutrients throughout our bodies, we can’t live without it. Most adults carry between 9 and 12 pints of blood.

Blood comes in four common "ABO types" – A, B, AB and O – with each of these also being either Rh-positive or Rh-negative. In addition to ABO/Rh, there are many other important substances on the surface of blood cells that sometimes require very precise matching between donor and patient – which is why we may sometimes focus on certain blood types to meet a patient’s special transfusion needs.

Some blood types are more common than others, but since blood cannot be manufactured, volunteer blood donors of all blood types are needed to donate regularly to help countless patients in need.

Learn about each blood type and if you're a BloodSource donor and don't know yours, login to MybloodSource to find out.

Blood Components

Your blood is made up of several different portions of what we refer to as "blood components." These include "red blood cells," "plasma" and "platelets" – each serving a specific purpose.

  • Red Blood Cells
  • Plasma
  • Platelets

Red blood cells

The most needed blood component, red blood cells transport oxygen through the body. Anyone experiencing severe blood loss for any reason needs red blood cells to survive.


Plasma is the liquid portion of blood. It's what suspends red blood cells, platelets, and other cells within our bloodstream. It also contains thousands of different proteins and other substances (electrolytes for example) that are needed for our bodies to function normally. Plasma transfusions are often critically needed by:

  • Burn and trauma victims
  • Some organ transplant recipients
  • People with certain rare blood disorders

Plasma donations can be frozen for up to one year prior to their transfusion into recipients. They also may be used to create a variety of medicines – such as albumin, clotting factors, and immune globulins – needed to treat patients with medical conditions including massive blood loss, blood clotting abnormalities (such as hemophilia), and immunodeficiency disorders.


Platelets are needed to prevent and/or stop bleeding. Not uncommonly, trauma victims, whose platelets are lost due to bleeding and related processes, require platelet transfusions. Heart surgery patients also are frequently transfused with this product owing to treatment-related loss, damage, and/or destruction of their platelets. Also patients battling leukemia and other cancers – especially if they undergo transplantation with bone marrow (or related stem cell sources) – will require transfusions to make up for their platelets that are destroyed by chemotherapy and/or radiation. Because platelets last for only 5 days after they are donated, a constant supply is vitally needed.

Schedule an Appointment

Schedule an appointment to give blood at one of our convenient BloodSource Donor Centers located throughout Northern and Central California.

Find out what type of donation is most needed at this time, call





There are many opportunities to donate blood and help patients in need. Learn about the different donation opportunities including whole blood, platelets and plasma.

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