Abstract
The Rh (Rhesus) blood group system is one of the most polymorphic and immunogenic systems known in humans. D antigen is the most immunogenic antigen in the complex Rh blood group system. Because of variability in expression, weaker forms of D antigen are encountered with regards to reactivity with antisera posing problems in blood banking. Weak D defines any D phenotype where D antigen is quantitatively weaker than normal. The importance of weak D lies in the fact that transfusion of weak D red cells to a D negative patient may result in alloimmunization or haemolytic disease of newborn in a sensitized pregnant woman.
The prevalence of Rh(D) negative and weak D varies worldwide. A total of 17,444 samples were tested for Rhesus status in the present study: the percentage of Rh(D) negative was 1.97 (346 cases) and the percentage of weak D was 0.578 among Rh(D) negative and 0.0114 of the total. The aim of the study was to find out the prevalence of Rh(D) negative and weak D among the blood donors of Manipur in North-Eastern India.

Key words: Alloimmunization, D antigen, Rh (D) negative, Weak D.