Many people learned about blood types sometime in school but may have forgotten a lot of that information. Let’s review some of the general principles so that you can better understand which blood types are rare, and why. 

Blood Types Review

There are four major blood groups: A, B, AB, and O. These are further divided into positive and negative by whether there is an Rh factor attached. This is expressed as either present (+) or absent (–). For example, a type A blood type person with no Rh factor is A- (called A negative).  

This system creates the eight most common blood types:

1. A-
2. A+
3. B+
4. B-
5. O+
6. O-
7. AB+
8. AB-

This point is where most people’s understanding of blood types stops. However, there are at least an additional 61 known antigens in the Rh system – which can create millions of possible combinations of blood sub-types. 

Common and Rare Blood Types

The most common blood type is O positive, followed by A positive. Ethnicity and family descent also play a big part in blood types and how common each type is in certain regions of the world. The following table is derived from broad data sets: 

Blood types that are rare include AB negative, which is the rarest of the eight main blood types – just 1% of donors have it. However, demand for AB negative blood is low and it is not difficult to find donors with AB negative blood.

Some blood types are both rare and in demand. This includes the Ro subtype, which is often used to treat people with sickle cell disease. O- blood is perhaps the most valuable blood in the world as it can be given to nearly any blood type (except when the person has some rare antigen outside of the main ones).

O- donors who are also cytomegalovirus (CMV) negative are extra special because their blood is safe to give to babies. CMV is a flu-like virus that most adults have been exposed to at some point in their life with mild effects, but the virus can be fatal to babies. 

The Rarest Blood of all

Rh-null blood is termed “Golden Blood”, and is the rarest type in the world, with only 43 known cases reported. RH-null occurs when the person’s blood lacks all of the 61 possible antigens. It is extremely useful because it can be donated to others who may have extremely rare blood types. Consequently though, individuals with Rh-null blood types can only receive blood from others with Rh-null blood. Because of this, Rh-null donations are used very sparingly, and are valuable for scientific research. 

Karen Stockdale, RN, has more than 20 years experience in healthcare. She is also a medical and technical writer and editor.