Du PHENOTYPE - A REVIEW

u is the phenotypic term used to denote a weakened expression of the antigen. u originally defined as those red cells reacting with anti-D only when a more sensitive indirect antiglobulin test was used. u phenotype can arise from three different genetic situations, a) A person may inherit a gene coding for weakened quantitative expression of u antigen, b) One gene may interact with another to modify and weaken the expression of the antigen, c) A gene may not code for the total material that makes up the antigen. The frequency of D' 1 antigen is relatively low less than 1%. D is a poor immunogen, however, accelerated destruction of u red cells can result if transfused to a person already making anti-D. Hence u donor units are currently labelled as Rah positive. u recipients are labelled as Rah negative. Newborn of Rah negative mother is tested for & u and Rh Ig is recommended for mothers of positive or u positive infants in order to prevent potential immunisation. The terms u variant or partial D' ; are recommended when there is both a qualitative and quantitative difference noted in the antigen.