Blood Group (ABO + Rhesus)

Blood Group testing determines your ABO blood type (A, B, AB, or O) and your Rhesus (Rh) factor (positive or negative), giving you a complete classification such as A positive, O negative, or B positive. These categories are based on the presence or absence of specific proteins, called antigens, on the surface of your red blood cells. Your blood group is determined entirely by your genetics and remains the same throughout your entire life, so this is a test you only ever need to have done once. Knowing your blood group is a valuable piece of personal health information for several practical reasons. Matching blood groups is essential if you need a blood transfusion, as receiving incompatible blood can cause a serious immune reaction. It is also important during pregnancy, particularly the Rhesus factor: if an Rh-negative mother is carrying an Rh-positive baby, a simple preventive treatment can be given to avoid complications.

Beyond these clinical situations, your blood group is simply an interesting fact about yourself. Think of the antigens on your red blood cells as a kind of identity badge. Your immune system is trained to recognise your own badge as friendly, but if blood with a different badge enters your system, your immune system may mount a defence against it. The ABO system has four main types: O has no A or B antigens (O negative is the universal donor), AB has both (AB positive is the universal recipient), and A and B each carry their own antigen. The Rhesus factor adds another layer, the D antigen, which is either present (positive) or absent (negative). Together, these create the eight common blood groups.

Nothing you eat, drink, or do in your daily life will change your blood group: it is hardwired into your DNA from birth. The distribution of blood groups varies across populations; in the UK, O positive is the most common (around 35 per cent of people), while AB negative is the rarest (roughly 1 per cent). Once you know your blood group, it is worth keeping a note of it with your personal health records. If you have any questions about what your blood group means for you, particularly if you are planning a pregnancy or have an upcoming medical procedure, your GP or midwife will be happy to talk it through with you.