Blood consists of formed elements (or blood cells) and blood plasma. Formed elements are erythrocytes (red blood cells), leukocytes (white blood cells) and platelets (or thrombocytes)

Blood groups and rhesus factor

Your blood group and rhesus factor are determined by genes inherited from your parents. A person can have one of the four blood groups: O, A, B or AB. It does not change throughout life.

In Latvia, blood group distribution is as follows:

A child inherits their blood group with a stronger (dominant) gene from their parents. The A and B genes are always dominant. If one parent has the A and the other parent has the B group, their child can have any of the four blood groups. If a child inherits the O gene from one parent and the A gene from the other, the child will have the A or the O group, but if the O gene is inherited from both parents, all children will have the O group.


Rhesus factor is determined by the presence of the D antigen on person’s red blood cells. Having the D antigen gives a person the positive Rh and a lacking it gives the negative Rh. Rh positive parents can have both Rh positive and negative children while Rh negative parents can only have Rh negative children.


Some facts:

  • Most frequently, there is not enough of Rh negative blood for transfusions because only 15% of people are Rh negative.
  • All blood groups and Rh are equally valuable!
  • In adults, the amount of blood is around 7% of the body weight (about 5 litres).
  • A healthy person has about 25 trillion red blood cells.
  • In a year in Latvia, donated blood allows making: 15 tons of packed red blood cells, 2.2 tons of platelet concentrate and 25 tons of plasma.
  • According to 2020 data, 1.64% of people in Latvia are regular donors.

The Rh system also has other important antigens, such as C, c, E, e, etc., which are determined in a process called phenotyping.

Determining donors’ Rh D antigen is very important. Sometimes when people have very weakly expressed D antigen they are defined as Rh positive donors and RH negative recipients. It means that if a transfusion is needed, they should receive Rh negative blood.