D antigen and Rh Blood Group

D antigen:
Another very important antigen tested for in the clinical lab is the D antigen. When a person’s blood type is referred to as A-positive, the positive is referring to the D antigen. A-negative would be an absence of the D antigen. The D antigen is also part of a larger group, the Rh blood group system. The Rh blood group system consists of many different antigens but Rh-positive and Rh-negative refer to the D antigen.

The D antigen is an important antigen in blood banking because it can cause HDN, hemolytic disease of the newborn, (more on this later) and is immunogenic meaning it can cause a strong reaction if for example Rh-positive blood is transfused to someone who is Rh-negative. Rh transfusion reactions tend to cause delayed hemolytic transfusion reactions (DHTR) with extravascular hemolysis.

The Rh group is a complex group of antigens caused by two genes, RHD and RHCE. RHD is responsible for the presence or absence of the D antigen and RHCE is responsible for C, c, E, and e (the other antigens that make up the Rh group). Over the years the Rh system has undergone many nomenclature changes due to new research and increased complexity. Since these antigens come from genes, there is a whole spectrum of possible phenotypes. One base pair change can cause different outcomes of expression.

For example, base pair changes in the Rh genes can cause a person to lack all Rh antigens (Rh null), or have weakened expression of Rh antigens (Rh mod). There are about 50 Rh antigens recognized by the International Society of Blood Transfusion (ISBT) but the beginning laboratory scientist can take a simpler approach to understand the basics. The two nomenclature systems most important for people just learning blood banking are the Wiener and Fisher-Race systems. It’s important to be able to use both systems interchangeably and if given one, be able to convert it to the other. These systems can be a bit confusing to remember so it’s best to have an easy system to quickly jot them down.

Wiener Nomenclature	Fisher-Race Nomenclature
R₀	Dce
R₁	DCe
R₂	DcE
Rz	DCE
r	dce
r’	dCe
r’’	dcE
ry	dCE

Study Tip
It’s easiest to memorize the Wiener nomenclature as it is in the table. When converting to Fisher-Race nomenclature write the D’s first, then the C’s, then the E’s. For the D’s it’s 4 caps then 4 lowercase. C’s alternate starting with lowercase, and E’s have 2 lowercase followed by 2 uppercase. Simply jot this down at the start of your test and you won’t have to worry about remembering what z, y, prime, and double prime mean. The bolded R₁ and r are the most common phenotypes.

Nerdy Note
The Rh group got its name from a lab experiment using rhesus monkey RBCs. Guinea pigs and rabbits were transfused with rhesus monkey RBCs and the antibody they produced was found to agglutinate 85% of human RBCs. At the time it was thought this was the same blood group causing transfusion reactions in the hospital even when ABO blood was matched correctly. The Rh name (after rhesus monkeys) was born and it stuck. It was later found that the antibody created from rhesus monkey RBCs and the antibody produced due to HDN and other transfusions were different but it is still called Rh to this day. The antibody produced due to the rhesus monkey RBCs was renamed anti-LW after the researchers who ran the guinea pig, rabbit, and monkey experiment (Landsteiner and Weiner).