Blood type transfusion can be considered safe as long as the serum of the recipient does not contain antibodies for the blood cell antigens of the donor. The "ABO system" is the most important blood-group system in human-blood transfusion. The associated anti-A and anti-B antibodies are usually "immunoglobulin M", abbreviated IgM, antibodies. ABO IgM antibodies are produced in the first years of life by sensitization to environmental substances such as food, bacteria, and viruses. The original terminology used by Karl Landsteiner in 1901 for the classification was A/B/C; in later publications "C" became "O". Type O is often called "0" ("zero", or
Jehovah's Witnesses and blood transfusions by failing to report any benefits of blood-based treatment. Nor do its publications acknowledge that in some situations, including rapid and massive haemorrhage, there are no alternatives to blood transfusions. He claims Watch Tower Society publications often discuss the risk of death as a result of refusing blood transfusions, but give little consideration to the prolonged suffering and disability, producing an added burden on family and society, that can result from refusal. Attorney and former Witness Kerry Louderback-Wood also claims that Witness publications exaggerate the medical risks of taking blood and the efficiency of non-blood medical therapies in critical situations.