A blood type (also called a blood group) is a classification of blood based on the presence or absence of inherited antigenic substances on the surface of red blood cells (RBCs). These antigens may be proteins, carbohydrates, glycoproteins, or glycolipids, depending on the blood group system. Some of these antigens are also present on the surface of other types of cells of various tissues. Several of these red blood cell surface antigens can stem from one allele (or very closely linked genes) and collectively form a blood group system. Blood types are inherited and represent contributions from both parents.

A total of 33 human blood group systems are now recognized by the International Society of Blood Transfusion (ISBT). The two most important ones are ABO and the RhD antigen; they determine someone's blood type (A, B, AB and O, with +, - or Null denoting RhD status). Read more ...

Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells of the body, and transports metabolic waste products away from those same cells. Read more ...

Pseudoscience - Rh-negative blood, present in about 15% of the population, is sometimes linked to extraterrestrial (ET) theories due to its unique absence of the Rhesus (Rh) protein found in other primates. While scientific explanations center on genetic evolution, some hypotheses propose ancient, non-human, or extraterrestrial genetic modification to explain this distinct blood type.

Multi-omics - Your blood may already know what illness comes next long before symptoms appear   ScienceX - May 15, 2026

Predicting who will develop common diseases is key to prevention, detection, and early treatment. Traditionally, clinicians have estimated risk based on age, sex, laboratory results, and lifestyle factors. Although these classical indicators provide important information, they do not necessarily reflect the multifaceted biological mechanisms underlying disease development.