Red cells of individuals with the Del phenotype possess an extremely low number of D antigen sites. Most commercially available anti-D reagents cannot detect these low numbers of antigens without employing an adsorption elution technique. This method requires incubating the cells with anti-D at 37o C. Successful elution of the adsorbed anti-D proves the presence of the D antigen. During routine testing, these individuals would most likely be identified as Rh(D) negative and receive Rh(D) negative blood products.
When definitive typing is needed, molecular studies can be employed to detect a mutant RHD gene that alters the expression of the RhD protein. This phenotype is relatively common in individuals of Asian ethnicity (10-30%) but is rare in whites.
