The principles and process of entering into proficiency testing programs is discussed under Chemical Testing (www.WaitroLabnetChemfilesLabnetChemProfTest). The reliability of a laboratory test result depends mainly on a combination of the accuracy of the performance of the equipment, the quality of the reagents and microbiological media and the performance of the analysts. The first of these parameters is observed by calibrating, using and maintaining the equipment, conducting intermediate checks on it, and keeping records of its performance. The quality of reagents and microbiological media are assured through quality control checks on the media, quality assurance certificates and adherence to stipulated storage, handling and discard conditions documented at purchase, and the bench practices. Analyst performance is normally monitored through intra-laboratory comparisons on testing and the performance of individual operations (weighing, delivering and diluting solutions, observing colors and colony counting).

Proficiency testing allows one to see how successful the combined application of the three types of activities has been, especially in the overall competency of the analysts—in general inaccuracies in the performance of equipment are easily detectable within the laboratory since they result in very high deviations from the expected test results. The variations in the performance of individuals (especially in microbiology, which requires high bench skills and measurements based on eye estimations and judgments) play an important role in deciding how close a test result is to the expected “true” value. Proficiency testing examines the latter aspect in recognizing the standard deviation observed for a given test in a laboratory.

In entering into a proficiency testing scheme it is important to select the tests most commonly performed and the food matrices more frequently tested in the laboratory.

Microbiological testing deals with living organisms which are continuously growing and highly susceptible to storage temperatures. The temperature and the duration of transport of samples therefore contribute the activity test cultures. This tends to be beyond the control of the laboratories and even of the proficiency testing service providers operating internationally. Participating in a proficiency testing scheme essentially involves the airlift of cultures, customs clearance and performing the tests on the expected day. Delays in the transport and customs clearance of test matrices containing live cultures, difficulties arising from non-adherence to storage temperatures in transport and storage leave can raise doubts about the validity of the test results, especially in the case of quantitative estimations. It is important that the proficiency test service provider and the laboratory participating in the testing scheme take note of these difficulties, communicate them to each other and design a means to minimize errors that may arise as a result.

Proficiency test results provide the best evidence for an accrediting body on the performance of the laboratories prior to any kind of assessment. However, it must be noted that good results in proficiency testing, which brings in a good rating for the laboratory, does not necessarily mean that the laboratory is meeting the high international performance standards. Judgment on the standard can only be made after close examination of performance at the site of the testing laboratory.