“We are linked by blood, and blood is memory without language” – Joyce Carol Oates.
The human body relies on blood to act as a transport system: it carries useful things like oxygen, nutrients and hormones around the body while removing harmful waste products and helping us battle infections. But did you know that not all humans have the same blood?
Our red blood cells are coated in antigens while antibodies are found in the serum and the presence or absence of these substances determine an individual’s blood type. The most common blood typing systems that are used are the ABO system (A, B, AB or O) and the Rh system (+ve or –ve).
The ABO typing system revolves around two antigens – A and B and two antibodies – similarly A and B. Using antigens, we can classify human blood into four groups: Type A, coated with antigen A, type B, coated with Antigen B, type AB, which is coated with both and type O, which is coated with neither. The antibodies present in the serum in the following way: Type A presents antibody B, type B presents antibody A, type AB presents with neither antibody and type O presents with both antibodies (Mitra et al, 2014.)
The Rh typing system revolves around the presence or absence of the Rh(D) antigen. Presence is signified by a +ve sign while absence is signified by a –ve. Thus, someone who is O– has red blood cells coated with neither A or B antigens, serum that contains A and B antigens and no Rh(D) antigen.
Blood typing is important as it helps prevent complications during blood transfusions. When antibodies and antigens of the same type come in contact, an agglutination, or clumping, reaction takes place. Transfusions are therefore safe as long as the antibodies in the serum don’t match up with the antigens present on the red blood cells.
However, there is a small subset of people who still have to be careful when receiving transfused blood.
These people have type hh, or Bombay blood, so named for the first place it was first observed by Dr. Y.M. Bhende in 1952 (Dean, 2005). Individuals with this blood type do not have antigen H, or the antigen that makes type O what it is. Hence, they cannot create antigens A or B since those are created from antigen H.
Much like people with type O blood, people with Bombay blood can donate to anyone but can only receive from those who share the Bombay blood phenotype. To prevent complications during transfusions, it is important to test thoroughly since the phenotype would show up as type O in most tests.
This phenotype is present in approximately 4 in 1,000,000 members of the population (0.0004%), and is found most commonly in the Indian subcontinent (India, Pakistan and Bangladesh) and Iran.
By Rhian Gray
Sources
Dean L. Blood Groups and Red Cell Antigens [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2005. Chapter 6, The Hh blood group. Available from: https://www.ncbi.nlm.nih.gov/books/NBK2268/
Mitra, R., Mishra, N., Rath, G.P. (2014 Sep-Oct). Blood groups systems. Indian Journal of Anaesthesia; 58(5): 524–528. doi: 10.4103/0019-5049.144645
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