Calibration procedures Laboratory Accreditation

The most powerful tool to minimise the component of variance due to error in the laboratory is the discipline which recognised accreditation schemes bring. They encompass all the likely areas which produce mistakes, documented procedures, training, checking procedures, control of samples, monitoring conditions, formal audits and perhaps above all calibration. The general quality movement has produced pressures to make laboratory accreditation commonplace and as more laboratories reach this status it must be expected that reproducibility will improve. In the current economic climate, a problem is finding sufficient laboratories able to devote sufficient time to precision trials. 

Each country has its own accreditation body for laboratories. In the United States, NIST is administering the National Voluntary Laboratory Accreditation Program (NVLAP) [109]. The criteria for accreditation used by NVLAP is consistent with ISO Guide 25, which involves the following items (1) quality system, (2) staff competence and training, (3) facilities and equipment, (4) calibration and traceability, (5) test methods and procedures, (6) recordkeeping, and (7) test reports. 

Obviously, at each stage of measurement there is some degree of uncertainty, and estimates of this uncertainty form part of the calibration procedure. It is perfectly acceptable for a laboratory to carry out its own calibrations, provided they maintain appropriate calibration standards and operate a suitable quality. system. However, it is often more convenient to buy-in calibration services. Wherever possible the calibration laboratory used should be accredited (UKAS or equivalent). 

The demand for higher quality has produced pressures to make laboratory accreditation commonplace, and as more laboratories reach this status it must be expected that reproducibility will improve. The calibration of test machines, training, documentation of test procedures, sample control, and formal audits all have an enormous influence, and the discipline involved in maintaining an accredited status helps to minimize mistakes and maintain reproducibility. International agreements undoubtedly widen the scope of accreditation schemes and ensure uniform levels of accreditation. This is found to have an influence on the standard of laboratories with a consequent improxement in interlaboratory comparisons. 

Quality in NDT depends upon a number of factors. Qualification of NDT personnel, technical state and correctness of choice of testing equipment, availability of approved working procedures of examination, calibration of NDT equipment have decisive importance among those factors of an NDT laboratory. Assessment of NDT laboratory competence is provided through accreditation in compliance with the EN 45000 series standards. 

Accreditation is a formal recognition that a laboratory is competent to carry out specific (types of) calibrations or tests [2]. After the use of validated and standardized methods, the introduction and use of appropriate IQC procedures and the participation in PT schemes, accreditation to ISO/IEC 17025 is the fourth basic principle related to laboratory QA in general [4]. Guidelines on the implementation of ISO/IEC 17025, including the estimation of MU (see also Section 8.2.2), are published in the literature and by official accreditation bodies such as Eurachem, CITAC, EA, Eurolab, and ILAC (see Table 1) [2,60, 80, 81,110]. It is worthwile to mention that accreditation, just like participance in PT schemes, does not necessarily indicate good performance of the laboratory [108]. 

Fig. 1 Metrological traceability and hierarchy of procedures and materials (according to ISO/IEC 17511). uc(y) Uncertainty BIPM International Bureau of Weights and Measures NMI National Metrology Institute ACL Accredited Calibration Laboratory MCL Manufacturer s Calibration Laboratory ML Manufacturer s Laboratory Mf Manufacturer...

Closely related to preventive action is the process audit. Such an audit is performed as part of a laboratory assessment for each test on the proposed scope of accreditation. Performance of a test procedure is observed relative not only to the requirements of the ISO 17025 standard (or ISO Guide 25) but also with respect to performing the ASTM or ISO test method properly. As a minimum, the laboratory must have properly calibrated equipment, the current test method, and trained testing personnel. In addition, a representative number of test demonstrations will reveal whether good laboratory practices are observed in sample preparation, using the correct test parameters and calculating the results. When operators and technicians accept responsibility through such demonstrations, they tend to commit to the quality process. Real improvement occurs with involvement at all levels. 

CRMs are an important tool for quality assurance and quality control in analytical laboratories. They are used for verification of accuracy and precision (i.e., reliability of the results of analysis, validation of analytical procedures, establishing measurement traceability, and calibration of measurement equipment). Use of CRMs is recommended by the ISO/IEC 17025 standard and therefore it is obligatory for those who wish to obtain and maintain accreditation of the laboratory. 

In a current developing standards document being considered for the international sterilisation community, under a section on Dosimeters , it is specified that each batch of dosimeters to be used must be properly calibrated. This entails either (1) irradiation of a user s dosimeter in a standards or accredited reference (secondary) laboratory, and subsequent appropriate evaluation by the user, (2) irradiation in a suitably designed irradiation geometry in the user s laboratory along with dosimeters issued by a standards or reference laboratory, or (3) use of a radiation field where the calibration is traceable to a standards laboratory, according to an acceptable accreditation procedure. 

In contrast, ACR emphasizes the quality control, calibration of the equipment, and technology used in the procedures, and accordingly has developed three modules - module 1 for oncology, module 2 for brain, and module 3 for heart. A PET center must apply for all modules that are performed at the facility. For accreditation, the facility is required to submit information on the quality control and quality assurance program, data collection, reporting, radiopharmaceuticals procedures, and laboratory safety, along with chnical and approved phantom images. So, all equipment in a PET center is required to be calibrated and tested for accurate functionahty for accreditation by ACR. 

Standard ISO/IEC 17025 2005 requires a laboratory to have quality control procedures for monitoring the validity of tests and calibrations undertaken. This means that laboratories must perform internal performance-based quality control checks in accordance with Section 5.9 of ISO/IEC 17025 2005 as it applies to every test, technology, and/or parameter within their scope(s) of accreditation in order to demonstrate compliance with accreditation requirements. Reference or fortified material containing known amounts of analyte, at or near the permitted limit or the decision limit (a non-compliant control sample) as well as compliant control materials and reagent blanks should preferably be carried through the entire procedure simultaneously with each batch of test samples analyzed. Ideally, the control samples should also be very similar to test samples and stable over time. The laboratory should maintain a sufficient amount of control material to last for a significant time period (preferably a number of years) and at suitable analyte concentrations. 

ISO/IEC 17025 1999 Accreditation is the formal recognition of the competence of a body or an organization for a well-defined purpose. In contrast with the ISO 9001 processes, accreditation of a laboratory to ISO/IEC 17025 involves assessment of the technical competence and capability of the laboratory and its personnel. In practice, it is the procedure by which a laboratory is assessed to perform a specific range of tests or calibration measurements. Specific areas examined include infrastructure and staff qualifications, in addition to checks that an adequate quality management scheme is in place. The accreditation covers the range of materials tested or analyzed, the tests carried out, the method and equipment used, and the accuracy or precision expected, and is specific to the facility and the test. 

CRMs are widely used to ensure both proper calibration and satisfactory use of the analytical methodology. When many laboratories use specific CRMs in a systematic way as part of QC procedures, consistency of data between those laboratories will be achieved. The main limitation in this respect is the frequent difficulty of obtaining CRMs appropriate to each type of analysis. This lack of supply is being address by an increasing number of secondary material producers, some of whom have already achieved ISO/IEC 17025 accreditation for production and certification of these references. 

---