Do you need to know your blood type?                       

                Military personnel know their blood type; it is imprinted on their dog tags. Is it important for the rest of us to know what our blood type is in case of emergency? Ordinarily it is not but life on the battlefield is different.

            There are three major blood groups known as the ABO system and it identifies substances on the surface of the red blood cell that can be identified using antibodies that react against them. Type O blood lacks these substances.  Another important designation is the Rh system, so named for the Rhesus monkey species in which it was discovered. The ABO and Rh systems are separate from each other so that an individual may be type A, B, AB or O and either Rh positive or Rh negative. Type O Rh positive is the most common; type AB Rh negative is the rarest, comprising about 1 percent of the population.

            In addition to these so-called major blood groups there are dozens of others. Some are named after the person in which they were first identified (Kell, Duffy, etc.) and others received labels based on other factors such as place names, etc.

            Movies and TV episodes that show blood flowing from the arm of the hero into that of a wounded person in dire straits are quite out of date. Except for unusual circumstances there is usually time for the treatment facility to prepare blood that is compatible with that of the victim.

            If you require a blood transfusion the hospital laboratory’s blood bank will perform a crossmatch to ensure that there is no adverse reaction from the donor blood. If you carry a dog tag, medical bracelet or a tattoo stating that you are A Negative, for instance, a crossmatch is still mandatory because of the possibility that one of the minor factors will produce a possibly life-threatening reaction. Even the designations of universal donor or universal recipient are not relevant except in unusual situations because of the possibility of reactions against one of the other factors.

                        All healthy adults should consider being blood donors. The pain of the needle insertion is minor and transitory but the value of that small inconvenience is enormous. A unit (about a pint) of donor blood is often used to harvest individual components such as red blood cells or clotting components that are used for specific needs.