Blood donations are essential for millions of people every day. In the United States alone, blood is needed every 2 seconds. In lower income countries, a majority of blood transfusions are given to children under 5 years old. Individuals with cancer or blood diseases like sickle cell anemia need multiple transfusions in their lifetime. This need is compounded by the short shelf life of blood. Blood only lasts up to 42 days. One of the most crucial blood components, red blood cells, only lasts up to 35 days. This review provides an overview of common blood categorizing systems, blood donation types, individuals that can be donors and the blood donation process.

BLOOD TYPES

ABO Group System
Blood can be categorized into four groups: A, B, O or AB. This categorization system is called the ABO group system. ABO designation depends on the type of carbohydrate sugars on the surface of red blood cells. These sugars are attached to an antigen on the cell surface called the H antigen. If the H antigen contains N-acetylgalactosamine, it is considered an A antigen. Individuals with A antigens only have type A blood. If the H antigen contains D-galactose, it is considered a B antigen. Individuals with only B antigens have type B blood. If the red blood cells have neither sugar attached to the H antigen, the blood is considered type O blood.

Over time, an individual develops antibodies against the antigens they do not have. For example, people with blood type A with have anti-B antibodies, and persons with blood type B will have anti-A antibodies. People with type O blood have antibodies against both A and B antigens. Individuals with AB blood do not have either antibody. These antibodies are located in the plasma, the liquid portion of blood, and attack any blood in the body with the corresponding antigen. Individuals with type A blood have anti-B antibodies which attack type B blood and vice versa.

Blood type determines what blood the individual can accept. Because type O blood does not have any antigens, it can be accepted by anyone. Thus, individuals with type O blood are called universal donors. Because people with AB blood have both antigens and no anti-A or anti-B antibodies, they can accept any type of blood. These individuals are called universal acceptors. In addition to type O, individuals with blood type A can only accept type A blood, while those with B can only accept type O and type B blood.

Approximately 42% of individuals have type A blood, 10% have type B, 44% have type O and only 4% have type AB.

Rh blood groups
Blood can also be categorized by the presence of the Rhesus (Rh) antigen or Rh factor. Rh factor is another protein that may or may not be present on the surface of red blood cells. Individuals with Rh factor are considered Rh-positive, while those without are Rh are considered Rh-negative. Rh status is usually inherited. Most people have the Rh factor on their blood cells. Individuals with Rh factors can receive both Rh-positive and Rh-negative blood, but those with Rh-negative blood cannot receive Rh-positive blood.

Blood type is typically labelled by both its ABO and Rh type. In the United States, the most common blood type is O+ (37%), followed by A+ (36%), B+ (8%), O- (7%), A- (6%), AB+ (3%), B- (2%), and AB- (1%).

Other antigens
Blood cells contain nearly 100 antigens. Many are checked prior to blood transfusion. It is important that as many antigens are compatible between the blood recipient and the donor blood to prevent the body from attacking the donor blood. Most antigens will not cause a significant immune response from the recipient’s body if it is incompatible, unless they are the Rh and ABO antibodies. Incompatibility of these two antigens can cause a severe reaction called a transfusion reaction.

BLOOD DONATION TYPES

There are multiple types of blood donation. The most common type is whole blood or blood donation. Other types include plasma, platelet and power red (or double red cell). Blood donation can also be made to specific people such as one’s self (autologous) or a friend or family member (directed).

Whole Blood
Whole blood is blood consisting of all blood components. These include red blood cells, white blood cells, platelets, and plasma. Red blood cells have hemoglobin which carry oxygen to various cells in the body. White blood cells, or leukocytes, are components of the immune system that fight against infections and foreign bodies. Platelets, also called thrombocytes, are clotting agents that stop bleeding by clotting along blood vessel lesions. Plasma is the yellow liquid component of blood, which makes up 55% of whole blood.

Most recipients of blood donation do not need all the components of whole blood. Thus one donation can help treat up to three different people. Whole blood can be donated every 8 weeks (56 days).

To provide a blood donation, the donor is asked a series of personal questions to determine the health and safety of their blood. The donor’s pulse rate, temperature, blood pressure and hemoglobin levels are also determined. If the donor is deemed suitable, blood is collected from a needle placed in the donor’s elbow into a plastic bag. The whole donation process takes about an hour, while the actual blood donation takes 10 minutes.

Blood donations can also be utilized to collect specific, essential blood components. These blood component donations are described in greater detail below.

Plasma
As mentioned above, plasma is the liquid portion of blood. It is made up of more than 700 components including proteins, hormones, blood sugar (glucose), electrolytes, oxygen and clotting factors. Plasma has multiple functions including serving as a protein reserve and maintaining electrolyte balance.

Donated plasma lasts much longer than red blood cells. When frozen, it can last for up to one year. Clinically, plasma is primarily used in treating coagulation conditions such as hemophilia and Von Willebrand disease. The components of plasma can also be extracted to make medical products that treat a wide variety of diseases such as immune deficiencies, respiratory disorders, angioedema, and neurological disorders. Plasma may also be used during surgery or to treat patients with severe burns. While plasma can be collected from whole blood donations, plasma donations have the added benefit that larger volumes can be collected at a time in larger concentrations.

Plasma donation is very similar to whole blood donation. The donor will be asked a series of personal questions to determine the condition and safety of the donor’s plasma. Plasma donors may also undergo a brief, free physical to ensure they are healthy. A sample of blood will also be tested to ensure that the donor has a sufficient protein and iron levels.

Plasma is collected through a process called plasmapheresis. Like in whole blood donation, a needle is placed in the donors arm and blood is removed from the donor. The blood is then separated into its component by a plasmapheresis or apheresis machine. The blood cells are then returned to the donor while the plasma is collected and frozen for later use. The plasma donation itself takes longer than whole blood donation, about 30-50 minutes. The whole donation process typically takes 1.5 to 2 hours.

Many plasma collection centers also compensate their donors. Compensation varies from center to center. Plasma can be collected every 28 days, up to 13 times a year.

While all eligible donors are welcome, plasma donations from individuals with Type AB blood are highly desirable. Because type AB blood does not contain any antibodies against A or B antigens, plasma from type AB donors can be used by patients with any blood type. Some blood centers will go as far as to only collect plasma from individuals with type AB blood for this reason.

Platelets
Platelets are small cells that clot along blood vessel injuries to stop bleeding. These cells are essential for individuals suffering from traumatic injuries or severe conditions such as cancer. Platelets can only be used up to 5 days after they are collected, making their donation extremely urgent.

Similar to a plasma donation, the donor undergoes an examination prior to donation. The blood is extracted from a vein in the elbow. The platelets are then separated during a process called plateletpheresis by a thrombapheresis orapheresis machine. The remaining blood is then returned into the donor’s other arm. Platelets can also be collected during plasma donation.

The platelet donation process typically takes 3 hours. Platelets can be donated every 7 days for up to 24 times a year.

Double Red Cell or Power Red
A power red donation collects two donations worth of red blood cells during one donation. During the donation, blood is collected from one of the donor’s arms and separated by an apheresis machine into red blood cells, plasma and platelets. The plasma and platelets, along with saline, are then returned to the donors other arm. This donation process allows for large quantities to be collected from a single donor. Since red blood cells are the most needed blood component of recipients requiring a blood transfusion, one donation can save several lives.

This procedure takes approximately 30 minutes longer than a whole blood donation, however collects twice as many red blood cells. Power red can be donated every 16 weeks (122 days).

There are different requirements for male and female donors. In order to be a power red donor, in addition to being healthy and at least 17 year old, male donors must be at least 5’1 (155cm) and weight at least 130lbs (59kg). Female donors must be 5’5 (165cm) and weigh at least 150lbs (68kg)

Autologous
Autologous donations are blood donations made for the donor’s personal use, like for a surgery. These donations can only be made with a prescription. Like with regular donations, these donations can only be made when the donor is in good health.

Rules for how often you can donate blood are different when an individual is making an autologous donation. There is no age limit for autologous donations. These donations can be made every 4 to 7 days or even in as little as 3 days before a surgery.

Donors are advised to avoid acetaminophen, aspirin, and alcohol 48hours before your donation. The donor may be prescribed iron supplements if his/her hemoglobin levels are low prior to donation, if necessary.

Currently, any blood donated for autologous use that is not used by the donor will be discarded.

Directed
Directed donations are blood donations made for a specific recipient, typically a family member or friend, that will undergoing surgery in the near future. Like with autologous donations, these donations can only be made with a doctor’s prescription. Although this is possible, there is no evidence that blood from recipient chosen donors is