RhDtyyppi

RhDtyyppi, or RhD type, refers to the presence or absence of the D antigen within the Rh blood group system on red blood cells. Individuals with the D antigen are RhD positive (RhD+), while those lacking the antigen are RhD negative (RhD−). The D antigen is highly immunogenic and central to transfusion compatibility and pregnancy management.

The RhD status is clinically significant because exposure of an RhD− person to RhD+ red cells can trigger the production of anti-D antibodies. This alloimmunization can cause hemolytic transfusion reactions in future transfusions and, during pregnancy, hemolytic disease of the fetus and newborn if the fetus is RhD+ in a subsequent pregnancy.

Genetically, the D antigen is encoded mainly by the RHD gene, with additional Rh antigens determined by the RHCE gene. D expression ranges from strong (RhD+) to weak (weak D), and some partial D variants can lead to anti-D formation if misclassified as RhD− in transfusion or pregnancy.

Typing is usually performed by serologic testing in blood banks, with molecular genotyping used in complex cases or where serology is inconclusive. Blood transfusion and organ transplantation require compatibility testing for ABO and RhD status; guidelines on weak D testing may affect whether a person is treated as RhD+. In pregnancy, Rh immune globulin (anti-D) is administered to RhD− mothers at risk to prevent alloimmunization.

Prevalence varies by population; approximately 15% of people of European descent are RhD−, while RhD+ is more common globally, with regional variation.