The surface of red blood cells contains markers that the immune
system can recognize—one of these markers is the Rh factor (Rh [D] antigen). A
person whose blood contains the Rh factor is Rh-positive (D); a person whose
blood does not contain the Rh factor is Rh-negative (d).
Blood type contains information about the presence (+) or absence
(–) of the Rh factor. Blood type is indicated by a letter (A, B, or O) and a
symbol (+ or –). If a person has B negative (B–) blood, for example, that
person is Rh-negative. A person with B positive blood (B+) is
Sarah Marshall, MD - Family Medicine & William Gilbert, MD - Maternal and Fetal Medicine
How this information was developed to help you make better health decisions.