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What are blood types and how do they mean?

by Bharti
Published: Last Updated on

So Blood type… What is it? You may already know that you are “O positive” or “B negative or the different combinations of A, B, O positive, negative etc. So what do these letters mean? How do they matter? Why are they important enough to be mentioned in identity cards like driving license etc.? Are they necessary for everyone to know? Too many doubts crowd the mind right? Well we hear about Universal donor, Universal acceptor. Why should we know about these? Well simply put, to know is knowledge; Knowledge is power and with power we attain the capability to save lives.

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Before venturing into the power aspect let’s take a Wonderland joy ride inside our body. Try to imagine we are teeny tiny surfers surfing our way through the blood stream. On the way we encounter red blood cells loaded with oxygen for transporting it to cells. During this whole period we are visited by our well-wishers “proteins, carbohydrates and fats”. Well these are obviously necessary for maintaining the structure and function of red blood cells.


ABO Blood Type

Among the array of wellwishers, the proteins are the signature marker of our blood types. These proteins are innate to our body determined by our genetics obtained through our parents. Well these proteins are named as antigens. These antigens stimulate the body to produce antibodies. Whenever the body encounters intruders it sends its soldiers “antibodies” to annihilate the trespasser antigens. Our blood stream may consist of antigens A, B, a combination of these AB or none referred to O. These antigens have a specific type of adornments in the form of carbohydrates which is very precise for each individual. This typing of blood based on antigens present is called ABO Blood Grouping. ABO blood grouping system was first pioneered by an Austrian scientist Karl Landsteiner in year 1909. The following table will summaries the blood typing.

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Blood Type Antigen in Red Blood Cells Antibody in plasma Receive blood From Donate Blood  To
A A Anti B A, O A,AB
B B Anti A B,O B,AB
O Anti A, Anti B O O,A,B,AB

Rhesus Type

There are other kinds of proteins called Rhesus type (Rh) which may be present termed as Rh Positive (+) or absent referred as Rh negative (-). So put together our blood type is essentially of 8 categories- A+, A-, B(+), B(-), AB+, AB-,O+ and O-. To elaborate let me provide an example. My blood group is O positive which means my red blood cells do not possess A, B or AB antigens but it contains the Rh factor protein. If somebody says that they are AB negative then it means they contain both A and B antigens in their cell surface while the Rh factor is absent. Because of the exact nature of blood groups not all can receive or donate blood during blood transfusion.


During emergency cases when blood need to be transfused to the patient it is very important to know the correct blood group of patient and donor. The patient has to receive compatible blood from the donor otherwise it will lead to agglutination of blood cells leading to death ultimately. Let me clarify this with an example. Say a patient with Blood group A is mistakenly transfused with Blood containing blood group B- his blood plasma already contains antibodies against antigen B (i.e. Anti B antibodies). These anti B antibodies start fighting with the B blood group leading to agglutination or clots. Once blood clots with in the blood vessels, it cannot flow easily triggering the immune system to destroy itself. This can be life threatening in extreme cases. During pregnancy it is very important to know the blood type of mother.  Thus it is very important to transfuse compatible blood to the patient.

Rh incompatibility could be observed during pregnancy when the mother’s blood type is in conflict with the fetus blood type. For example if the mother is Rh negative and the fetal blood is Rh positive then she might develop auto immune response to the fetus attacking it. The immune response is slow to develop during the first pregnancy. Subsequent pregnancies can lead to higher risk.

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Universal Donor and Universal Recipient

During emergency life saving cases people having Blood group O negative can donate blood to all since they do not possess any antigens in their cell surface. Hence the hence they are called as Universal donors.

During emergency cases people possessing AB+ blood group can receive blood from all since the cell surface has necessary antigens. Hence they are called as Universal Recipient.

            In both the cases immune system of the patient is not compromised leading to a promising recovery from blood loss.

Testing for Blood types

Blood test is performed in a biochemical lab to know blood types

Technician mix an individual blood with a variety of serum (clotting agent removed) samples. The technician will monitor an individual’s blood reaction with each serum. The antibodies in the serum will react differently based on the type of blood sample. For example, if the serum consists of blood type A it means it has Anti B antibodies reacts with the blood clotting it then the person has B blood group.

Blood types in India

Based on the recent reports the most common blood type prevalent in India is B+ (38.14%) followed by O+ (27.85%), rarest being AB- (0.49%) followed by O- (1.43%).

Rarest Blood group in the world

There are more than 200 rare blood types in the world. However the Rhnull blood group is considered as the rarest blood type in the entire world. In this blood type none of the Rh antigens are present in the blood. It is called as Golden Blood. It was first found in an aboriginal Australian woman in 1961.