It is essential that everyone know their own blood group and that of their family members. There are many occasions when knowing your blood group could be important, for example, if you or a member of your family required an urgent blood transfusion it would be useful to know your blood group in advance. If it was an uncommon group it would allow the hospital valuable time to ensure adequate supplies. Travelling overseas carrying a blood group card could prove invaluable. Accidents and other emergencies can often be dealt with more efficiently knowing the blood group of the person or persons involved. There are 4 main blood groups - A, B, AB and O, of which group O is the most common (47 percent of population). The blood type is determined by proteins called antigens found on the surface of red blood cells. If you have the antigen A on the red blood cells then you have got type A blood. When B antigen is present, you have type B blood, when both A and B are present, you have type AB blood. When neither are present you have type O blood. Another blood group system involves Rhesus factors. The name Rhesus comes from the Rhesus monkeys in which the protein was first discovered. Rhesus factor D, the most important, is found in the blood of 85 percent of people, they are known as Rhesus positive. The remaining 15 percent are Rhesus negative. So people can be classified according to both systems, for example AB positive or O negative. We have also included 1 extra lancets free of charge in this pack. The reason for this is that the lancet that is included by the manufacturer is a single use lancet and if you accidentally click the button before you are ready or do not get enough blood then the whole test will be ruined. Including an extra lancet with each test means that if this does happen, you have a spare lancet and can still perform the test :) The colour of the lancets may vary from the one shown in the picture.