Type O Negative blood (also denoted as Type O -) is just one of thirty or so different blood types spread amongst the human population. Type O Negative blood is one of the 8 blood types that are by far the most common. These 8 blood types are A Positive (A+) , A-, B+, B-, AB+, AB-, O+, and O-. The other blood types are for the most part rather rare.
Basics of Blood - So just what does having O negative blood mean in the general scheme of things? Let's go back to the beginning, always a good place to start. The blood of course is the medium which transfers nutrients from our heart to cells throughout our body, and on its return trip, carries away waste materials from the cells to the kidneys and liver, where the waste is disposed of. The blood is itself made up liquid (plasma) and blood cells, and these cells may contain certain antigenic substances, called antigens. The blood cells will contain different types of antigens in different people. The word antigen is a derivative of the word genetic, and your blood type is determined by genetics, in other words, your blood type is inherited. The nature of an antigen is that its presence will cause our immune system to produce antibodies to fight it. The immune system will not create antibodies to fight antigens that are recognized as having a natural presence in your body, i.e., antigens that “belong”.
Types A, B, And AB - If you have Type A blood for example, your blood cells contain antigens your immune system recognizes as being friendly, and you can accept Type A blood from another donor. Your blood serum however contains antibodies against Type B antigens. The antigens associated with Type B blood are recognized as being foreign, and the antibodies in your blood serum will attempt to destroy any Type B blood cells which enter your body. Similarly a Type B individual has Type A antibodies in his or her blood serum and cannot accept Type A blood through transfusion. A person with Type AB blood has both A and B antigens, but has no antibodies in the blood serum so can accept Types, A , B and AB blood.
How Is Type O Different? - So where does Type O come in? We'll get to the Type O negative blood later. Those with Type O blood have neither A or B antigens in their blood, but have A and B antibodies in their blood serum. This means that people with Type A, B, or AB can receive blood from a type O person, but the Type O person, having A and B antibodies, cannot accept blood Types A, B or AB. To put it another way, if you have Type O blood, your body will only accept blood from another Type O individual.
As far as blood transfusions go, the Type AB person is the fortunate one. Having no A or B antibodies, they can accept A, B, AB, and O blood and are sometimes referred to as "universal recipients". Those with Type O blood on the other hand, are in a sense the good guys. Many people can use their blood, and on the case of Type O negative blood, everyone can, they are the "universal donors".
The Rh D Factor, Nailing Everything Down - Now that you have the ABO Group down pat, let's get on to the positives and negatives. There is another group of antigens that some people have and some do not, called the Rh D antigens. If your blood has these antigens you are Rh D Positive (Rh D+), if not, you are Rh D Negative (Rh D-). The Rh factor is particularly important as far as pregnant women are concerned. If a woman is Rh D - and is exposed thorough transfusion to Rh + blood, her system may develop Rh D antibodies which, in crossing the placenta can affect a fetus having an RHD+ blood type. These antibodies can then create problems in the fetus, sometimes mild, sometimes severe, and often not until after birth. (continued...)