While not the most common antigen, K (also called Kell or KEL1) is the third most immunogenic human RBC antigen and the second most major cause of HDFN after RhD, with an approximate prevalence in the general population of .0001-.006% (compared to RhD-HDFN at ~0.5%) [1,10,11]. This evidence concerns the gene KEL and rheumatic heart disease.