Quick Guide

Blood typing is a routine procedure used in cases of blood transfusions, organ transplants, and during pregnancy. This laboratory test aims to detect specific inherited substances called antigens found on the surface of red blood cells, categorizing them into four primary groups: A, B, AB, or O, which is referred to as the ABO system.

Additionally, another system, known as the Rh system, determines whether red blood cells are Rh-positive or Rh-negative. If you possess the Rh factor, you are considered Rh-positive. It’s crucial to ascertain both ABO and Rh types because a mismatch between them can trigger a strong immune response, potentially resulting in a life-threatening reaction.

About the Test

What Is Blood Group Test?

This test determines an individual’s blood type or their specific blood group classification. People do not share the same blood group universally, as there exist numerous distinct types, with some being more prevalent than others.

When your blood group matches that of another person, both individuals consider themselves “compatible,” enabling them to give each other blood when necessary.

Why Is Blood Group Test Done?

Typically, this process is carried out to determine an individual’s blood group affiliation. Various scenarios warrant such knowledge:

• Organ transplants or blood transfusions necessitate compatibility checks to ensure a safe match between donor and recipient.
• During pregnancy, it is crucial to assess the compatibility of the mother’s and the child’s blood to safeguard both their health.
• When donating blood, knowing your blood type is essential to ensure a secure transfusion.
• Newborn infants are screened for specific diseases by undergoing blood typing tests.

What does the test tell us?

Specific markers called antigens, located on the surface of red blood cells (RBCs), determine blood types. The two main antigens on human RBCs are A and B, with another crucial one called Rh. A blood typing test identifies the presence or absence of these antigens, establishing both your ABO blood group and your Rh type.

In this classification:

If your red blood cells contain A antigens, you belong to blood group A.

When your red blood cells contain B antigens, you are classified as blood group B.

If your red blood cells carry both A and B antigens, you fall into blood group AB.

When your red blood cells lack both of these antigens, you are categorized as blood group O.

The presence of the Rh protein on your red blood cells denotes Rh-positive blood, while its absence indicates Rh-negative blood.

Naturally, our bodies produce antibodies against A antigens for blood type B individuals and against B antigens for blood type A individuals. Blood type AB individuals do not generate antibodies against either A or B. Consequently, AB+ individuals can safely receive AB+, A+, or B+ blood. Conversely, those with blood type O will have antibodies against both A and B.

The following table outlines the expected antibodies associated with each blood type:

Blood Type	Antibodies Present
A+	Anti-B Antibodies
B+	Anti-A Antibodies
AB+	None
O+	Anti-A and Anti-B
A-	Anti-B Antibodies
B-	Anti-A Antibodies
AB-	None
O-	Anti-A and Anti-B

These antibodies play a crucial role in determining a person’s blood type and their compatibility with different blood types.

 For instance, individuals with blood type A have antibodies that target the B antigen. If they receive a transfusion of type B blood, their antibodies may attack and destroy the transfused B+ red blood cells, potentially leading to severe and life-threatening complications. Therefore, it’s of utmost importance to match a person’s blood type with the blood they receive during a transfusion.

Rh factors, on the other hand, follow a genetic determination. A person can inherit the Rh factor from one or both parents. Unlike antibodies against A and B antigens, the body does not naturally produce antibodies against the Rh factor. Instead, they only emerge when an individual lacking the Rh factor on their red blood cells is exposed to Rh-positive red blood cells.

This exposure can occur during pregnancy or childbirth when the mother is Rh-negative and the baby is Rh-positive, or in cases where an Rh-negative individual receives a transfusion of Rh-positive blood. In either scenario, the initial encounter with the Rh antigen may not trigger a strong immune response, but subsequent exposures, such as in a second pregnancy, can lead to severe reactions.

Blood Type Test Method

Method: Hemagglutination

Sample: Whole Blood EDTA

Container/Tube: Pink top (EDTA)

Process

The process used to ascertain a person’s ABO blood group involves two essential steps:

Forward Typing: Assessment of blood sample is done in a laboratory by introducing it to two solutions. One solution contains antibodies against the A antigen (Anti-A), and the other holds antibodies against the B antigen (Anti-B). The reaction of blood to these antibodies indicates the presence of specific antigens. If the blood cells clump together (a process known as agglutination) when exposed to anti-A antibodies, the person is classified as blood group A. If there is a reaction with anti-B antibodies, it signifies blood group B. If no reaction occurs with either, it indicates blood type O.

Reverse Typing: In this step, the mixing of plasma (the liquid part of the blood after separating white blood cells and red blood cells) with type A blood first and then separately with type B blood is done to observe the reaction. This step helps confirm the results obtained in the forward typing process. Both reverse and forward typing must align to determine the blood type accurately.

Additionally, there’s a separate test for Rhesus (Rh) blood typing:

Rhesus Typing:

This test determines the RhD blood type by mixing a small sample of red blood cells (RBC) with a lab solution containing RhD antibodies. If the blood agglutinates, it is designated as Rh-positive; if no reaction occurs, it is classified as Rh-negative.

Major hospitals use both the ABO and RhD blood typing procedures as standard for all donated blood and transfusions. In some cases, additional testing may be required to identify other red cell antigens, especially in individuals with rare blood disorders.

References:

1. https://www.mayocliniclabs.com/test-catalog/overview/113490
2. Blood typing testing. (2022). Retrieved from https://www.testing.com/tests/blood-typing/ 
3. Portea Medical, & Dr. Udaya Kumar Maiya. Retrieved from 

https://www.portea.com/labs/diagnostic-tests/blood-group-abo-rh-171/