The conundrum of blood typing


By Hiya Islam


Pulsating 24/7 through a vast network of blood vessels, the blood ensures the survival of every living cell in the body. We are accustomed to seeing this vital liquid in red, but it also comes in blue, green, yellow, colourless and what not, in other creatures. The differences exist due to diverse respiratory pigments in action, such as haemoglobin and haemocyanin. In spite of that there is a certain feature of blood that beguiles the mind, the mystery of letters defining our blood.

The ABO blood typing system is how we can group human blood into A, B, O and AB types. There are chemicals called antigens on the surface of erythrocytes aka red blood cells that act as surface markers. These antigens are genetically inherited. Presence of B antigen makes an individual a type B. The same applies to type A crews as well. But, AB types have both A and B antigens while O types do not bother to carry around any antigens.

A body always reacts or, to be specific, produces an immunological response when a foreign antigen gains access in the body. For this reason, each type of blood comes with specific antibodies. To illustrate, type A is protected by the company of anti-B antibodies. So, whenever type B blood flows defiantly in the bloodstream, say owing to reckless transfusion, these blood cells are attacked by the antibodies.

In addition, type AB carriers do not have any antibodies as both antigens are present in contrast to type O who has antibodies against A and B antigens. The blood grouping conundrum does not end here. There’s still more to explain; the affair of negative and positive blood. This brings a new antigen in the scene- Rhesus (Rh) antigen. There are many Rh antigens and amongst them ‘D’ is very common. If D antigens are found on erythrocytes, then the blood is said to be positive, otherwise it is negative.

Now, after the interpretation of blood types, what’s left is their procedure for determination. The easy way to find this out is to mix the patient’s blood with 3 reagents which are the antibodies for A, B and Rh antigens. If blood agglutination or clotting is seen, then the antigen in blood reacts with the very antibody in the reagent. Suppose, the blood reacts with anti-B and anti-Rh then it can be deduced that the blood type is B+.

As stated before, the body’s defence mechanism protects the body from foreign invasion by a special response. Although blood transfusions of the wrong type are rare, the consequences can prove to be fatal if symptoms like fever, blood in urine, back pain, jaundice are unnoticed for long. Extensive blood clotting, kidney failure and strokes are a few deadly outcomes. Also, the donated blood may carry diseases. This is why donated blood is thoroughly screened for HIV, syphilis, hepatitis-B and so on and packed with proper labelling.


Hiya Islam is a student of BRAC University.

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