The human MHC class I chain-related gene A (MICA) is located within the HLA class I region of chromosome 6. The expression, structure and function of MICA differs considerably from classical HLA class I genes. MICA proteins are considered to be markers of 'stress' in epithelial and endothelial cells, and act as ligands for cells expressing a common activating natural killer cell receptor (NKG2D). MICA molecules are highly polymorphic and the functional relevance and implications of their polymorphism in transplant rejection, autoimmune disease and cancer are emerging. MICA antibodies have been implicated in cases of humoral solid organ rejection. MICA genotyping uses luminex technology to type MICA alleles. The test targets MICA sequence polymorphisms defined by DNA-typing methods. MICA typing can be helpful in determining whether patients are matched or mismatched for MICA with their donors.