BLOOD TYPING

Discovery of blood groups:

  People were familiar with transfusion of blood for so many years before the discovery of blood groups, though sometimes that resulted to death. It was 1901,when the Austrian Karl Landsteiner first described about blood grouping that made blood transfusion far more safer.

Transfusion of blood between two individuals can lead to blood clumping or agglutination as well as some toxic reactions that may be fatal for the patient sometime leading to death. That blood clumping is an immunological reaction of antigen antibody interaction was first discovered by him, who later made the typing of blood possible and thus made blood transfusion more scientific. For this discovery Karl Landsteiner was awarded with the Nobel Prize in 1930.

Different blood groups:

Our Blood types is determined by the specific types of antigens (relatively large protein molecules) present on our red blood cells. There are 27 known human blood groups, for which each of us can be typed. As a result, there is one or more antigens for each of these blood groups. Since many of these blood systems also are found in apes and monkeys, it is likely that they evolved prior to the time that we became a separate species.

The 27 known human blood groups:

The antigens are located on the surface of the red blood cells and in the blood plasma there are antibodies, which distinguish particular antigens from others, causing bursting or agglutination of the red cells when foreign antigens are found by binding to the antigens. Individuals have different types and combinations of these molecules. The blood group we belong to depends on what we have inherited from your parents.

The AB0 and Rh systems are the most important ones used for blood transfusions. Not all blood groups are compatible with each other. Mixing incompatible blood groups leads to blood clumping or agglutination, which is dangerous for individuals.

The ABO blood typing:

There are four different kinds of blood types: A, B, AB and 0 (null), according to the AB0 blood typing system.

Type A blood group contain type A antigen on the RBC cell, and type B contain type B antigen.AB type blood have both the antigens on the RBC. The designation of O was supposed to mean that no antigen, i.e. no A or B type antigen was present on the red blood cells. Later it was discovered that the type O cells actually had another antigen which was named H (for "human").

Blood type is determined by the "alleles"(different possible types of a particular gene, in this case the gene(s) controlling our Blood type) which we inherit from our parents. There are three common Blood type alleles: A, B, and O. Everybody has two alleles, one inherited from each parent. The possible combinations of the three alleles are: OO; AO; BO; AB; AA; BB

Blood types A and B are known to be "codominant" alleles (in our genetic Blood make-up both of them have important controlling influence), while O is "recessive." A codominant allele is apparent, or dominant, even if only one is present; a recessive allele is apparent only if two recessive alleles are present. Since Blood type O is recessive, it is not apparent if the person inherits an A or B allele along with it.

Therefore, there are certain possible allele combinations in a particular Blood type:

(1) OO = Blood type O; (4) AB = Blood type AB;

(2) AO = Blood type A; (5) AA = Blood type A;

(3) BO = Blood type B; (6) BB = Blood type B.

Blood transfusion will be successful if the person going to receive blood has a blood group that doesn't contain any antibodies against the donor blood's antigens. But if the person going to receive blood has antibodies matching the donor blood's antigens, the red blood cells in the donated blood will result to clumping.

Rh –factor blood grouping:

Further typing as (+) or (-) is based on the Rhesus factor (Rh antigen) present on the red blood cells. People having Rh antigens on RBC are Rh positive (+) & who lack the factor are Rh negative (-). However, most people are Rh positive.

The +ve or -ve characterization depends on the presence or absence of two Rhesus genes called the D or d, inherited from each parent. A person is Rh (D) -ve if he/she has inherited a d gene from each parent making them d/d. In case of a person being Rh(D) +ve there may be three genetic combinations possible, like the offspring has got D gene from each parent making them 1)D/D or a D and d from the parents (either ones) making them 2)D/d or 3)d/D.

Thus it is possible to have an Rh (D) -ve offspring from a father who is Rh (D) +ve and mother who is Rh (D) –ve and vice versa. If one of the parent (Rh (D) +ve) has both a D and d gene and the other is Rh (D) -ve; the offspring may be Rh (D)-ve if he /she inherits the d gene from his (Rh (D) +ve) parent. The child from a D/D father and D/d or d/d mother or vice versa will always be Rh(D) +ve since it will get a D from one of his parent and either a D or a d from the other. So, what is relevant here is the presence or absence of the D gene that makes a person Rh (D) +ve or Rh (D) -ve.

…Now, the problem is that the D antigen present in the Rh (D) +ve blood stimulates the Rh (D) -ve blood into producing antibodies against it. Whereas Rh (D) +ve blood does not produce antibody against a Rh(D) –ve blood group , as +ve blood does not produce `anti-d` - there is no anti-Rh(d). However the problem comes as the Rh (D) -ve blood produces antibody against Rh (D) +ve.

According to above blood grouping systems there are 8 following blood groups.