UAS accredits proficiency testing providers on the basis of the ISO/IEC 17043 standard.Proficiency testing involves the use of inter-laboratory comparisons for the determination of laboratory performance. PTP’s ensure that all samples have precisely the same composition and that the results obtained are processed in the correct way.Calibration laboratories, test laboratories and medical laboratories regularly have to take part in proficiency testing. For a proficiency test various laboratories are sent the same sample, which could be blood, sludge or drinking water for example. The composition of the sample is known to the organiser. The laboratories test the sample and send their results to the organising party who then checks whether the results are mutually comparable and reports on this to the participants. This guarantees that a laboratory produces reliable results. The need for ongoing confidence in laboratory performance is not only essential for laboratories and their customers but also for other interested parties such as regulators and accreditation bodies.