Analysing blood under a microscope reveal some important and quite distinct differences. It was an early 20th century Austrian scientist by the name of Karl Landsteiner that first identified and subsequently classified these differences, and we know today that blood type is what defines each of us in terms of compatibility. Mixing two incompatible blood types resulted in a rapid coagulation (clotting) and many early experiments in blood transfusions demonstrated this was a fatal condition. So what are these different types of blood, and how are they different?
There are two major differences in human blood type, and these relate to the type of unique chemical molecules that are present on the surface of red cells. Landsteiner called these two A and B types, that is; red blood cells having only A molecules became type-A, blood with B became type-B, cells with a mixture of both were labelled type-AB and finally cells on which neither molecules were observed were labelled type-O. This classification system is what we call today the A-B-O system with which all blood types fall into one of the three, or combinations of the three.
From this important discovery, blood transfusions became possible and with a significant success rate however there were still some unexplained reactions and fatalities that required more investigation. In 1937, the culmination of study in the field of reactions during blood transfusions, Karl Landsteiner working with Alexander Wiener discovered another critical aspect of compatibility named after the Rhesus monkey used in experiments. It was this Rhesus factor or Rh, as we now know it, causing many of the unexplained reactions during transfusions despite the care in which matching blood types were used. Interestingly, this discovery was tantalisingly related to the field of genetics, and some important discoveries lead to future developments in advanced medicine.
The Rh factor is classified as positive or negative, and blood types were subsequently suffixed with a +ve or ve Rh factor in groupings. Research today continues however in a given population, the ratio of blood types per 100 head in population is considered as 84 being Rh positive and 16 being Rh negative. Of these:
38 are O+ and 7 are O-
34 are A+ and 6 are A-
9 are B+ and 2 are B-
3 are AB+ and 1 will be AB-
Blood transfusions today are commonplace, and further advances serve to identify and categorise new subsets to ensure the safety of recipients. The advent of AIDS put considerable pressure on blood banks to develop methods identifying blood in which this virus is present. The risk of disease or complications during blood transfusions and surgery today are low, and we have the dedicated research and achievements of those early pioneers to thank for this life-saving discovery