Blood typing and cross matching test results are determined based on the reaction between the antigens and antibodies. An antigen causes the body to launch an attack against a foreign body and is known as an immune response. The attack begins when the body builds a special protein called an antibody. This antibody is uniquely designed to attack and nullify the foreign attack. In general a person's body makes antibodies only against foreign bodies and not against its own antigens.
Among the various antigens present in a person's body, the antigens found on the surface of red blood cells are important because they determine the person's blood type. When red blood cells having a certain blood type antigen are mixed with serum containing antibodies against that particular antigen, the antibodies attack and stick to the antigen. This is seen as clumping, formation of clump of cells while testing is done in a test tube.
For typing blood, a person's blood cells and serum are mixed in a test tube along with commercially prepared serum and cells. Clumping refers to the type of antigens or antibodies present and helps in determining the person's blood type. While cross matching blood, the patient's serum is mixed with cells from donor blood that may be used for transfusion. Clumping or lack of clumping in the test tube tells whether or not the blood is compatible.
There are over 600 known red blood cell antigens that are organized into 22 blood group systems. However routine blood typing and cross matching generally involves only two systems namely:
Blood typing helps in determining the blood type a person has. ABO system is used to classify the blood type. There are four main categories under the ABO system:
Blood typing also helps in determining the Rh factor of the blood. People who have the Rh protein in their blood are termed as Rh + (positive) and ones without it are termed as Rh – (negative). The Rh type is useful in deciding the blood type a person can safely receive during transfusion.
Blood type of a person is inherited and there is no normal or abnormal type. The blood type of a person is determined by checking out the following:
Type A: If the blood cells of a person agglutinate with Type A serum then the person has A blood type.
Type B: If the blood cells of a person agglutinate with Type B serum then the person has B blood type.
Type AB: If the blood cells of a person agglutinate with Type A and Type B serum then the person has AB blood type.
Type O: If the blood cell of a person does not agglutinate with Type A or Type B serum then the person has O blood type.
Understanding back typing
People with type A blood will have anti-B antibodies. People with type B blood will have anti-A antibodies. People with type O blood will have both. So if the person's:
Blood clumps only when B cells are added then the blood type of the person is A.
Blood clumps only when A cells are added then the blood type of the person is B.
Blood clumps in both cases the blood type of the person is O.
Blood does not clump when both types of blood are added then the blood type of the person is AB.
Understanding Rh results
1. If the person's blood clumps together when anti-Rh serum is added then the person is Rh+.
2. If the person's blood does not clump together when anti-Rh serum is added then the person is Rh-.
Blood typing and cross matching results
There is no normal or abnormal result. However the result may make us understand the following:
Bombay Blood Group
The Bombay blood group was discovered fifty years ago in Bombay as it included varied phenotypic characteristic when compared to the standard blood typing such as A, B and O. The RH factor of the blood groups were studied to understand the antigenic structures based on which the H antigenic characteristic became very important. The phenotypic characteristic of Bombay blood group was hence discovered as Oh wherein the 'h' represents its varied nature when compared to the other blood groups.
Bombay blood group contains 'h' characteristic. The RBCs are not agglutinated by the anti-A, anti-B. Bombay Blood group is not restricted only to Indians but is noticed among Caucasians, Japanese etc. Only about 0.01% of the world population has the Bombay blood group, which makes it an essential need to maintain a record of the respective blood type individuals for emergencies.
It is very easy to assume the blood group as O if the blood cells do not agglutinate with A and B antigens. However this may lead to adverse reactions such as hemolytic transfusion rejection when the respective blood group is transfused in to the patient. Confirmatory tests are essential to identify Bombay blood group - as the protein containing H antigen clearly differs from the O blood type. Therefore confirmatory tests such as anti-H lectin Ulex Europaeus are used to detect the presence of A ,B and OH types in the RBCs but does not agglutinate the Oh type.
Niemann pick is a type of lysosomal storage disease and is an inherited condition that involves the metabolism of lipids. This leads to a breakdown in the of use and transport of fats and cholesterol in the body. The disease affects the body's ability to mobilize fat within cells. When this fat (cholesterol and lipids) accumulates in large amounts, it causes dysfunction of the cell and untimely death of a person. Harmful levels of lipids accumulate in the spleen, lungs, liver, bone marrow and brain. Niemann pick disease is more common in children. The disease is classified into three major types namely Niemann pick A, B and C. Niemann pick Type A and Type B are caused by the deficiency in an enzyme called acid sphingomyelinase. This enzyme is found within the lysosome cells and is an essential component in metabolizing a lipid called sphingomyelin.
Symptoms are related to the type of disease.
Type A: occurs in children. Children may not survive as the condition affects the nervous system. Symptoms include:
Type B: occurs in childhood, known as the non-neurological type as the nervous system is not affected. Children survive into adulthood.
Type C: can occur in children or in adults
Other general symptoms include:
Diagnosis depends on the type of Niemann pick disease
For Type A or B: Blood sample or bone marrow sample is used to measure the level of acid sphingomyelinase in the blood.
For Type C: A small sample is skin is taken to test how the cells move and store cholesterol.
Other tests may include brain MRI, genetic testing and eye test to confirm if there is difficulty in normal eye movement
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Bibliography / Reference
Collection of Pages - Last revised Date: January 29, 2020