RhDnegative

RhD negative refers to the absence of the D antigen on the surface of red blood cells within the Rh blood group system. The D antigen is the most immunogenic component of the system, so the presence of D defines RhD positive status, while its absence defines RhD negative. The trait results from the absence or inactivation of the RHD gene on chromosome 1, typically due to gene deletion or other mutations.

Across populations, about 15% of people of European descent are RhD negative, with lower frequencies in many Asian and African populations. Testing to determine RhD status is usually performed by serology; some individuals show weak D or variant D forms that may require specialized testing to determine true RhD status. In clinical practice, RhD status guides blood transfusion compatibility and management of pregnancy.

RhD negative individuals can form antibodies to the D antigen if exposed to RhD positive blood through transfusion or during pregnancy. Such alloimmunization can cause hemolytic transfusion reactions and, in pregnancy, hemolytic disease of the fetus and newborn if the fetus is RhD positive. Prophylactic Rh immunoglobulin (RhIG) is given to many RhD negative pregnant people and RhD negative individuals undergoing RhD positive transfusions to prevent sensitization.

Historical note: The Rh factor was named after the Rhesus monkey in early experiments by Karl Landsteiner and Alexander S. Wiener in 1940. The D antigen is the most clinically significant component of the Rh system.