Most proficiency testing is carried out by means of proficiency testing schemes (PTS). The main features of PTS are:
- Test samples are distributed regularly to a number of participating laboratories, who then return the results of their analyses to the scheme co-ordinator within a specified time.
- Test samples are homogeneous, to ensure that any differences in results between laboratories due to the test sample itself are minimised.
- The levels of target analytes in PTS test materials are realistic, and will normally represent levels usually measured by most participating laboratories.
- Test samples are, as far as is technically possible, matrix samples of a similar type to those routinely analysed by most participating laboratories.
- The results from all laboratories will be statistically evaluated by the co-ordinator, to a pre-defined set of agreed criteria, and the performance of the laboratories published in a report.
- The confidentiality of participants in a PT scheme is maintained by identifying laboratories only by a unique code number. The co-ordinator does not disclose confidential information to any third party.
PT therefore enables laboratories to monitor their measurement capability both by comparison to peer laboratories, and over time within their own laboratory. Laboratories are recommended to take action when they obtain unsatisfactory performance in a PT scheme. This will usually involve investigating the cause of the poor results(s), and then taking corrective action, where appropriate. In most PT schemes, participants are able to seek confidential advice from the co-ordinator in the event of poor performance to assist with this procedure.