Methods for histocompatibility testing in the early 21st century

Purpose of review In recent years there have been major improvements in methodology behind three mainstay clinical human leukocyte antigen (HLA) tests: HLA phenotyping, panel reactive antibody screening and cross matching. Recent findings First was the appearance of flow cytometry crossmatching; subsequently molecular HLA phenotyping and solid phase panel reactive antibody screening arrived, which were shown to be far more accurate and precise than previous techniques based on complement-dependent cytotoxicity. HLA antibody specificities identified by solid phase panel reactive antibody and antigen frequencies soon will be used by the US United Network for Organ Sharing to calculate panel reactive antibody in allocating allosensitization points. Clinical correlation of flow crossmatch increases by combining interpretation with solid phase panel reactive antibody data. Donor-specific antibody identification by solid phase panel reactive antibody is being applied as a virtual crossmatch to facilitate patient and lab management. Donor-specific antibody monitoring is also a means to gauge immunologic reactivity toward the allograft in various scenarios, such as desensitization, assisting diagnosis and treatment of humoral rejection, tapering immunosuppression. Summary This review discusses the evolution of clinical HLA testing methods from the standpoint of evolving and improving laboratory practice and patient care.