There's more to blood group types than A, B, AB, and O. There's' a blood group, hh or Bombay blood group, which is so rare that many physicians go their entire career without witnessing a single patient with this blood type.

The Bombay blood group is rare and treating patients with this blood type also comes with its own challenges. Consider the common blood groups.

Blood group A has antigen type A and antibody type B,  Blood group B had antigen type B and antibody type A, Blood group AB has both antigens A and B but no antibodies, Only blood group O has antibodies A and B and no antigens.

A rare difficulty- Quick facts about Bombay blood group

• Globally, 1 out of 2.5 lakh people have this blood group.
• The blood group hh can donate blood to any group but accepts only hh blood type.
• A preliminary test of this blood type may incorrectly identify it as O+.
• Advanced Immuno-Hematology testing is needed to detect this blood group.
• It's highly improbable to readily find this blood group at any blood bank.
• The RH- sub-variety of hh blood group is the hardest to find.

A mix-up with O blood group

Generally, a blood test includes the process of gauging the presence and absence of antigen/antibodies in the blood. As the Bombay blood group has neither A nor B antigens, it can be wrongly identified as O blood group.

If patients with Bombay phenotype receive blood group O red cells or any other blood group red cells except the Bombay group, they may develop an acute hemolytic reaction. This reaction can cause acute renal failure or disseminated intravascular coagulation (DIC) which is associated with high morbidity and mortality rates especially in unconscious patients who may receive large volumes of incompatible blood before signs of hemolytic reaction appears. (Asian J Transfus Sci. 2013 Jan-Jun; 7(1): 86–87.Hayedeh Javadzadeh Shahshahani, Mohamad Reza Vahidfar, Seyed Ali Khodaie).

In a recent paper (The Bombay blood group: are we out of risk?), the authors Dipta TF and Hossain A state, " As because in our country there is routine practice of "only forward or cell type grouping" using finger prick method by voluntary blood donors organization and various blood banks; so there is tremendous chance of misinterpretation or unexploration of this Bombay blood group. When misdiagnosed, this Bombay group can cause fatal haemolytic transfusion reaction." 

They further suggest incorporating "routine serum typing or reverse grouping confirmation" along with 'O' cell control in reverse grouping procedure in every Transfusion Medicine Department or Blood Bank or Blood Donor Centers to reduce the risk of fatal haemolytic transfusion reaction.

Mumbai-based paediatrician Dr. Shilpa Inamdar says, "Not all blood banks know how to employ correct blood grouping practices when it comes to Bombay blood group. Further, she informs that when a Bombay blood type patient is assumed to be having O blood group and is administered blood accordingly, it's not always that adverse reactions may take place."

How to procure Hh blood group

• First, ask the patient's relatives to get tested as there is a decent chance one of them might be sharing the blood group.
• While checking with local blood banks, do get in touch with the ones in big cities too.
• Spread the word about the requirement on social media and local FM stations. Ask blood banks to connect you with WhatsApp groups of blood donors for help in this regard.
• Get in touch with NGOs or visit www.bombaybloodgroup.org, a website set up by an NGO.

The Bombay connection

The hh blood group was first discovered in Bombay in 1952, thus the name Bombay blood group. However, there's another reason for this moniker.

Globally, one person out of 2.5 lakh people is estimated to have hh blood group whereas in Mumbai, for every 10,000 people there’s one person who has this rare blood group running in their veins. The reason for high concentration of such people in Mumbai is said to be intra-community marriages.

A study on the prevalence of Bombay blood group, published in Asian Journal of Transfusion Science in 2015, found that India had 179 cases of Bombay phenotype. Of them, 112 were found in Maharashtra, 14 in Karnataka, 8 in Andhra Pradesh, 6 in Goa, and 5 in Gujarat. Prevalence of this blood type is comparatively rare in north India.

This story was contributed by Sonali Desai, a Mumbai-based freelance writer and a member of 101Reporters, a pan-India network of grassroots reporters.