A practical guide to proficiency testing for clinical histocompatibility laboratories

Proficiency testing (PT) is a critical and mandatory element of the quality assurance (QA) program in histocompatibility laboratories, serving as a key mechanism for verifying the accuracy and reliability of clinical testing. Under the Clinical Laboratory Improvement Amendments (CLIA), laboratories testing U.S. patient samples must participate in PT for the regulated analytes listed in Subpart I of the CLIA regulations. Most assays performed in histocompatibility laboratories are non-regulated; nonetheless, CLIA still requires laboratories to assess the accuracy of all testing, regardless of regulatory classification, and the American Society for Histocompatibility and Immunogenetics (ASHI) further requires PT participation for any analyte reported by an accredited laboratory. Over time, changes in PT practices and the growing diversity of testing platforms and methodologies have introduced new challenges in PT implementation, reporting, and interpretation. Here, a workgroup convened by the ASHI Professional Standards Division presents a set of clarifications, guidelines, and best-practice recommendations to help clinical histocompatibility laboratories navigate PT requirements and achieve regulatory compliance. Throughout, we advance a single unifying principle: PT samples should be handled, tested, and reported in the same manner as clinical patient specimens.