THE MNS BLOOD GROUP

The FRCBS determines the blood group of each donor for three common blood group systems (ABO, Rh and Kell). However, there are several dozens of other known blood group systems. Blood groups are based on the characteristics of the surface structure of red blood cells (RBCs). We all inherit the genes that determine our blood type from our parents.

The MNS blood group system

The MNS blood group system belongs to those blood group systems which are not routinely determined prior to each donation. Analysing the surface structure of red blood cells in more detail, including MNS antigen determination, is only required when a patient needs an exact blood type match. For example, when a patient has produced antibodies against red blood cells following a transfusion or during pregnancy.

The significance of MNS antigens for RBC function is not yet fully understood. These antigens are negatively charged and it has been suggested that they play a role in maintaining a normal RBC distance. S and/or s and U antigens of the MNS blood group antigens are found in the RBC surface structure of almost everyone. Among the Finnish blood donors, no-one completely lacks the U-antigen. When a person completely lacks the U-antigen, his or her blood type is U-negative. This is a very rare blood type. People whose blood is U-negative have inherited the gene that controls this characteristic from both their mother and father.

Geographical breakdown

Among Finnish donors, the gene mutation causing the complete lack of the U-antigen has never been identified in donors of Finnish descent. However, it does occur in people of African descent. This rare blood type seldom occurs on other continents.

Clinical significance

Being U-negative is not related to any disease or medical condition. According to some studies, U-negative people have red blood cells that are resistant to a parasite causing malaria (Plasmodium falciparum). This finding, however, could not be verified in all of the studies. Being U-negative bears no significance to a person's health - it is merely a rare characteristic of the RBC surface structure and virtually only plays a role in blood transfusions.

Blood transfusions

When red blood cells that are not U-negative are introduced into the circulation of a U-negative person, his or her red blood cells start to produce antibodies (anti-U antibodies) against the MNS antigens he or she lacks. Typically, this occurs during a blood transfusion. In women, these antibodies may also be produced during pregnancy.

Whenever a U-negative person has produced anti-U antibodies, this should be taken into consideration in the case of a blood transfusion. This is because anti-U antibodies are known to be capable of causing the haemolysis (destruction) of transfused red blood cells (haemolytic transfusion reaction), if the transfused cells are not U-negative. Anti-U antibodies that have been passed from mother to foetus/newborn may cause red blood cell haemolysis, resulting in anaemia in the child. This condition is known as neonate haemolytic disease of the newborn.

The production of anti-U antibodies is best prevented in advance. Blood components from U-negative donors are collected and earmarked for U-negative patients prior to surgical operations. Due to this process, should a blood transfusion be necessary during surgery, the U-negative patient will not be exposed to foreign red blood cells, and - as a consequence - the production of antibodies can be avoided. This is particularly important for patients with severe sickle-cell anaemia necessitating frequent blood transfusions.

U-negative red blood cell components

The FRCBS does not have U-negative red blood cell components in stock. U-negative donors are summon to donate blood for a specific patient. Sometimes, rare U-negative blood components must be ordered from abroad. To ensure that U-negative blood components can be earmarked for a specific patient prior to an operation, we would be very grateful if all U-negative donors would only donate blood when summoned to do so.

How to locate U-negative donors?

We know that only people of African descent are U-negative. For this reason, we request an additional blood sample from all of our donors of African descent and screen the sample for this blood type. If the screening test implies that the donor is U-negative, we will ask for a new blood sample. This sample is tested in detail to determine whether the red blood cell characteristics are U-negative. If these tests confirm the blood group to be U-negative, the donor will receive a blood grouping card for people with a rare blood type. This card is useful when planning a surgical operation for a person with a rare blood type. The attending physician will be able to contact the FRCBS in advance to arrange for the delivery of the appropriate blood components.

The U-negative blood group is inherited

Belonging to the U-negative blood group is a recessive trait. This means that a person who is U-negative must receive the same rare gene from both of his or her parents. Because it is inherited, we ask all our U-negative donors for permission to contact their sisters and/or brothers to test them for rare blood groups as well. Among the siblings of a U-negative donor, approximately one in four is U-negative. This is important to the person concerned, should he or she ever need a transfusion. Additionally, it means that they can donate blood to other U-negative patients. In most cases, the parents and children of a U-negative person are not U-negative.