Blood Types: What Are They And What Do They Mean?

There are four blood types, each of which determines the amount of antigen present in red blood cells. The most common type is ABO.

When we go for medical checkups, it’s common to be asked our blood type, especially if we’re undergoing surgery or donating blood. Although it’s summarized in one or two letters, blood type indicates the proteins we have in our red blood cells, which can be lifesaving.

Blood is made up of red blood cells, white blood cells, plasma, and platelets. Blood type depends on the antigens on the surface of the red blood cells,” explains Carlos Castillo, a general practitioner. Each person’s blood type depends on the genes they inherited from their parents.

Antigens are molecules that have several functions, including transporting molecules into and out of the cell, maintaining the structure of red blood cells, and detecting unwanted cells that could cause disease.

“These antigens are proteins and sugars that our body uses to determine whether these red blood cells belong to us. Therefore, it’s important that when receiving a blood donation, it’s the right type, otherwise it could cause a rejection reaction,” Castillo adds.

What are the blood types?

Around 1900, pathologist Karl Landsteiner mixed several blood samples to determine which ones were compatible. He then classified four groups using the ABO typing system, which separates them according to the types of antigens on red blood cells and antibodies in plasma.

Alejandro Ortega, an internist, explains that there are two systems, ABO and RhD, for determining blood type. Currently, there are four ABO groups:

• Type A: The surface of red blood cells contains antigen A, and the plasma has anti-B antibodies.
• Type B: The surface of red blood cells contains antigen A, and the plasma has anti-B antibodies. 
• Type AB: Red blood cells have both A and B antigens, but plasma contains neither anti-A nor anti-B antibodies. This group can receive any blood type.
• Type O: Plasma contains anti-A and anti-B antibodies, but the surface of red blood cells does not contain A or B antigens. Anyone can receive this blood type.

Blood test

The way a person’s blood type is determined is through a blood sample.

The blood sample is mixed with antibodies against type A and type B blood. The sample is then tested to determine whether the blood cells are compatible. If the blood cells remain together, it means the blood reacted with one of the antibodies, according to the MedlinePlus website.

The reverse blood test is then performed. The liquid part of the blood is mixed with a type known to be type A or B. People with type A blood have anti-B antibodies. People with type B blood have anti-A antibodies. Type O blood contains both types of antibodies.