Proficiency-testing process

There is one element within the proficiency test process that causes difficulties for many of the participants. The proficiency-testing scheme trains participants to not report chemicals that are considered irrelevant within the scenario of the test and which, in real off-site analysis, could reveal confidential information that is considered not relevant in the context of the CWC. A review on how the test scenarios were applied revealed that participants are not really in a position to judge the relevancy of chemicals. It rather should be the Technical Secretariat making a final decision on the relevancy of chemicals instead, and, for that reason, accept the reporting of any chemical given that it is a degradation product of a Scheduled chemical or directly related to a Scheduled chemical. 

As the use of RMs increases and international trade in these materials becomes established, it has become clear that they can be subject to high levels of import duty and delay when clearing customs. In 1998 ISO/REMCO established Task Group 6 to investigate the problems involved in shipping reference materials (and materials that are in the process of being made into reference materials, such as proficiency testing materials) across national boimdaries. 

All proficiency testing schemes should have a statistical protocol which states clearly how the data will be processed and how laboratory performance will be evaluated. This protocol should also describe how the assigned value for any parameter in a test sample is estimated. This is an important consideration, as the performance of individual laboratories is gauged by comparison with the assigned value. 

Controls are used to ensure proper technique and the specificity of the stain. The use of similarly processed positive and negative staining controls is essential for interpretation of immunohistochemical reactions and must he done for each anti-hody. These controls may he commercially prepared, previously tested patient samples or proficiency testing specimens for which results have heen confirmed. 

The NVLAP is comprised of a series of laboratory accreditation programs (LAPs), depending on what is requested and what is needed. Each LAP includes specific calibration and/or test standards and related methods and protocols assembled to satisfy the unique needs for accreditation in a field of testing or calibration. NVLAP accredits public and private laboratories based on evaluation of their technical qualifications and competence to carry out specific calibrations or tests. All are based on the ISO/IEC Guide 25 discussed in Section 2. The process involves an application and the payment of fees. This is followed by an on-site assessment. If deficiencies are found, these must be resolved to the satisfaction of the assessment team. The laboratory then participates in proficiency testing (Section 5.7) and a technical evaluation. 

To assure that the best technology is available and that personnel are qualified, forensic science laboratories should undergo accreditation processes with periodic proficiency testing. This will assure some uniformity in procedure among different laboratories, and provide assurance that samples are analyzed correctly and data are interpreted accurately. 

Recognizing that heading off a potential problem is usually better (cheaper and less embarrassing) than coping with a nonconformance, the standard requires the laboratory to engage in preventive actions. This is defined as a proactive process to identify opportunities for improvement. The use of trend and risk analysis of proficiency testing data (see chapter 5) is mentioned as a possible preventive action. 

Residue-testing laboratories might also need to review their sample preparation processes and consider modifying or eliminating tissue homogenization prior to residue extraction. Suppliers of proficiency-testing services should also question whether certain drugs are appropriate to include in such studies. For example, liver spiked with sulfaquinoxaline, sulfadiazine, or sulfamerazine is not suitable for preparation of spiked interlaboratory check samples or reference materials. 

Quality control of laboratories depends on the availability of CRMs, round-robin studies, intercomparisons and proficiency tests between methods and between laboratories. Of special importance is a full knowledge of the complex analytical process and the painstaking pursuit of the true value by defining all sources of errors and the application of an adequate error source budget. The application of Poisson and Bayesian statistics could have some advantage. 

Process in reasonable control the indirect proficiency test will be most economical of resources when the participating laboratories are consistently producing PT material lots having good quality. This condition facilitates use of the ratio methods mentioned in the previous section of this paper, and thus reduces the number of accurate, traceable measurements that are required. 

Laboratory accreditation bodies also offer formal recognition (accreditation) of proficiency testing providers to ILAC-G13 2000 (International requirements for competence of providers of proficiency testing schemes). This process is intended to provide confidence that proficiency testing schemes are designed and conducted to internationally acceptable standards. 

Through the use of voluntary, anonymous proficiency testing, assess the analytical accuracy of criminalistics laboratories in the processing of selected physical evidence ... 

The initial procedures for the conduct of official OPCW proficiency tests have been developed by the Special Task Force on Analytical Issues in the period 1994 to 1996, and subsequently recommended for adoption through Working Group B to the Conference of States Parties the respective procedures were adopted by the First Conference of States Parties in May 1997 (5). The evaluation criteria have been further developed since, through consultation with participants in the proficiency-testing scheme. These consultations were often initiated by practical problems posed during individual proficiency tests. The numerous amended documents have recently been compiled into three comprehensive quality system documents that describe the process of the OPCW proficiency test, which has been accredited by the Dutch accreditation body in 2001 ... 

Figure 1. Process of the OPCW proficiency-testing scheme...

The process of the official OPCW proficiency test is shown in Figure 1. 

Only chemicals that are considered relevant within the scenario of the proficiency test are to be reported to avoid irrelevant chemicals being reported, in real off-site sample analysis, confidential information on the facility under inspection is revealed (e.g. information on an industrial production process that is not relevant to the implementation of the CWC). This requirement is a consequence of Paragraph C.17 of the Confidentiality Annex of the CWC, l1. The reporting of irrelevant chemicals is penalized with immediate failure of the test see Section 6.1. 

The process of evaluation, scoring, and designation of the OPCW proficiency-testing scheme is shown in Figure 22. The process is known to have three weaknesses, the areas of weakness are highlighted in Figure 22 and summarized in the following ... 

The selection of an analytical technique and the development of procedures and operating conditions are only one part of the process for achieving reliable measurements. Among the first steps of the validation figure the assessment of the method precision this parameter must be assessed between analysts and days. Appropriate precision, although necessary for reliable work, is not sufficient to guarantee accurate results Evaluation of sample matrix effect, development, and analysis of spiked samples, analysis of Certified Reference Materials (CRM) of similar composition for which the Pb concentration has been established by other laboratories and comparison of results between laboratories (proficiency testing) are equally important [13]. 

Ion-selective electrodes (ISEs) represent the current primary methodology in the quantification of S-Li [11-13], Moreover, ISE modules are parts of large and fully automated clinical chemistry analysers. In practice, the validation parameters are most often chosen in terms of judging the acceptability of the new measurement system for daily use. For this reason, the first approach was to study whether the detected imprecision fulfilled the desired analytical quality specifications. Secondly, proficiency testing (PT) results from past samples were of great value in predicting future bias. The identity of the three ISE methods was evaluated using patient samples. The analytical performance was checked after 6 months routine use. Without any exception, method validations always mean an extra economical burden. Therefore, the validation parameters chosen and processed have to be considered carefully. 

Westgard JO. Charts of operational process specifications ( OPSpecs charts ) for assessing the precision, accuracy, and quality control needed to satisfy proficiency testing performance criteria. Clin Chem 1992 38 1226-33. 

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