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What is a Blood Group Test?

A blood group test is a blood test that determines blood type by detecting the type of antigen present on the surface of red blood cells (RBCs). There are over 33 different blood types, and the most common method for blood grouping is the ABO typing. It characterises blood groups based on the presence of antigen A or antigen B in the blood in addition to the Rhesus (Rh) typing. Rh typing is characterised by the presence of antigen D.

Blood grouping is not a diagnostic test, as it does not help in diagnosing a disease; it is a basic test that detects the variant of blood group.

  1. Why is Blood Group Test performed?
  2. How do you prepare for a Blood Group Test?
  3. How is a Blood Group Test performed?
  4. What do the results of a blood group test indicate?

A blood group test is performed to evaluate the type of antigen present on RBCs. As per the ABO blood group system, our RBCs have either or both antigen A and B. A person with blood group A has antibodies against antigen B, and a person with blood group B has antibodies against antigen A. Similarly, a person with blood group AB does not produce antibodies against either of the antigens while an O type blood group produces antibodies against both the antigens.

If a person having blood group A is transfused with blood group B, it can lead to a severe immune response causing anaemia and jaundice, which is known as a mismatch transfusion. Moreover, if a person with blood group A is transplanted with an organ from a donor whose blood group is B, it can lead to an immune reaction in the form of graft rejection, ie, the transplanted organ is damaged and destroyed by antibodies present in the blood of the recipient.

Thus, a blood group test is performed:

  • To evaluate the type of blood, ie, A, B, AB or O
  • Before blood transfusion, to check for recipient compatibility
  • Before organ transplantation, to check for recipient compatibility
  • In pregnant women, because antigen D (or Rh factor) determination is important for evaluating mother’s and baby’s Rh factor; if the mother is Rh negative and foetus is Rh positive, it can lead to severe reactions and risk of miscarriage; in such cases, pregnant women are given certain medications to help sustain the foetus.

Thus, a blood group test is predominantly performed to ensure that one can safely receive or donate blood or organs.

No special preparations are needed for this test.

It is a simple test that takes less than 5 minutes. An experienced laboratory specialist collects a blood sample from your arm by inserting a small needle into a vein. A small quantity of blood is withdrawn into a sterile vial or a test tube. There is a momentary pricking pain when the needle is inserted into the vein.

Though this test is completely safe, it may lead to pain, light-headedness and bruising at the site of injection in some people. However, most times, these symptoms disappear quickly. Rarely, an infection may occur at the site of injection.

Results of a  blood group test are available within a few hours. Presence of antibodies against specific antigens helps in determining the blood type, eg, a person with blood group A will have antibodies against B antigen, and the Rh-negative blood group will have antibodies against antigen D. The table below will help interpret the presence of antigen and antibodies on RBCs and blood, respectively.

Blood Type (antigen on RBCs)

Antibodies present against antigen

A

B antigen

B

A antigen

AB

Neither antigen

O

A & B antigens

 

Presence of these antibodies in blood helps in deciding a person’s blood type and the type of blood he can safely receive, which is known as compatibility. This also helps in determining whether a person can accept an organ graft (or transplant); A person with:

  • A blood group can receive blood from a person with A blood group and O blood group
  • B blood group can receive blood from a person with B or O blood group
  • AB blood group can receive blood from person with A, B, AB or O blood group (Person with AB blood group is known as universal recipient)
  • O blood group can receive blood from person with O blood group only (Person with O blood group is known as universal donor)

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. This information is purely from an educational perspective and is in no way a substitute for medical advice from a qualified doctor.

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References

  1. Ranadhir Mitra, Nitasha Mishra, and Girija Prasad Rath, Blood groups systems. Indian J Anaesth. 2014 Sep-Oct; 58(5): 524–528.
  2. American Pregnancy Association: Rh Factor
  3. The American National Red Cross. Understanding Your Blood Type
  4. Chernecky CC, Berger BJ. Type-and-crossmatch – blood. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. Philadelphia, PA: Elsevier Saunders; 2013:1133-1134.
  5. Goodnough LT. Transfusion medicine. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders
  6. MedlinePlus Medical Encyclopedia: US National Library of Medicine; Blood Typing