Proficiency testing (PT), also called external quality assessment (EQA), was introduced into laboratory medicine more than 60 years ago as an educational tool to address observations that results for aliquots of the same sample were different when measured by different laboratories.

The measurement procedures used at that time were laboratory developed and differed among laboratories in implementation and calibration details. PT/EQA results were used to stimulate standardization of procedures and calibrators to achieve more uniform results among laboratories.

PT/EQA programs have evolved in scope and sophistication and are now an essential component of a laboratory's quality management system. PT/EQA is intended to verify on a recurring basis that laboratory results conform to expectations for the quality required for patient care. PT/EQA is a component of laboratory accreditation requirements in many countries.