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Background information - PTs, QC, method validation
Classification of interlaboratory studies
There are three broad categories of interlaboratory studies:
Proficiency Tests
They take place regularly, with a minimum of 12 participating laboratories. There are no prescriptions with respect to the method to apply. The aim is the determination of z-scores as a measure of laboratory performance. The relevant international standard is ISO 13528 (in Germany: DIN 38402 A 45). The organiser is usually a PT-provider, that is to say, a relatively small independent firm which offers this service and whose main source of income is the laboratory fees.
Internal (in-house) quality control (analytical quality assurance)
A minimum of 2 laboratories is required, with parallel in-lab measurements and evaluations where appropriate. The primary objective is the determination of systematic deviations across all samples and of in-house precision data. Secondary aims are the collection of raw data and methods comparison. There is no applicable national or international standard. The organiser is usually the quality assurance department of the company in question. Very often, quality control studies are not distinguishable from method-development programs, especially in middle-sized companies where method validation and development are not pursued separately.
Methods validation (collaborative studies)
A minimum of 8 participating laboratories is usually required (in the case of factorial studies, 4 laboratories are sufficient). The relevant standard is ISO 5725. The organiser is usually contracted by a state institution, or at least in the context of a program financed with public funds (e.g. in Germany through LFGB ยง64 or in the EU inside a EURL or through DIN or CEN).
