Trueness verification in European external quality assessment schemes: time to care about the quality of the samples.

An external quality assessment (EQA) survey on 14 fresh-frozen, single-donation sera assigned with reference measurement procedure (RMP) values revealed a mean bias of + 5.2% and + 3.7% for the cholesterol oxidase and the photometric glucose oxidase procedure groups, respectively. Conversely, on lyophilized sera, the same procedure groups showed almost bias-free results, the differences from the RMP values being only -0.8% for cholesterol and + 0.7% for glucose. These data, which are in fairly good agreement with the literature, suggest the existence of artificial matrix effects in processed materials. Therefore they indicate that, currently, assessment of trueness is hampered in many European EQA schemes, as most of them use lyophilized sera. This approach may give a false impression about the trueness of laboratory results as well as carrying the risk that laboratories calibrated on the RMP values of the survey samples could make errors in patient testing. Consequently, if European EQA is willing to fulfil a post-market vigilance function of the performance of in vitro diagnostic medical devices, then the time has come to tackle the problem of the quality of the survey samples. EQA organizers urgently need to make an effort to seek out materials that analytically behave like authentic clinical specimens. In the meantime, alternative approaches should be used. Although not ideal, the special survey described in this article is one of the possibilities. Naturally, it implies logistic problems and increased costs for the individual EQA schemes. However, both can be overcome with the cooperation of the predominantly nationally organized schemes.

Survey of serum potassium reference measurements.

We compared the quality of reference measurements for serum potassium in four reference laboratories from three different European countries, using a panel of 60 native patients' samples. The reference methods were based on either ion chromatography (one laboratory) or flame atomic emission spectrometry (three laboratories). Performance specifications for serum potassium measurements were defined as a maximum overall coefficient of variation (CV) of 1.5%, a maximum bias of 0.65% and a maximum total error of 3.0%. The overall imprecision for all laboratories was in the range of 0.7 to 1.3%, and was thus below the proposed specification of 1.5%. However, two laboratories reported 12 and 13 quadruplicates with CVs exceeding this limit. The mean bias (expressed as deviation from the overall mean of all laboratories) for all reference laboratories was < 0.65%. In the lower concentration range, however, one laboratory exceeded this limit. No laboratory measured samples with a total error above 3.0%. From these results, it can be concluded that the reference measurements, and, thus, also the reference methodologies, based on ion chromatography and flame atomic emission spectrometry were equivalent, and able to satisfy current analytical specifications for serum potassium measurements.

Current stage of standardization of measurements of specific polypeptides and proteins discussed in light of steps needed towards a comprehensive measurement system.

We present a standardization model for the measurement of specific polypeptides and proteins, which is based on an integrated development of all important elements of a reference measurement system. Generally, the model is in line with other current recommendations. However, it puts special emphasis on the definition of the analyte and on the role of reference methods for verification of the standardization process by measurement of patient specimens. Further, we discuss the needs for its implementation in the routine laboratory. In the light of this model, we investigate the current stage of standardization of routine methods for enzymes, peptide hormones, proteins, apolipoproteins, glycohaemoglobin, and tumour markers.

"Ocean-to-Ocean Project": a transcontinental external quality assessment trial in clinical chemistry realized throughout Eurasia.

More than 800 diagnostic laboratories situated throughout the Eur-Asian continent--from the Pacific Coast up to the North Sea littoral--were involved in a common survey of External Quality Assessment (EQA). It consisted of the simultaneous measurement of up to 30 analytes of 'general' clinical chemistry using the same batch of control material. The laboratories were associated in four EQA institutions: SKZL (The Netherlands), OQUASTA (Austria), SEKK (Czech Republic) and BKKSystem (Community of Independent States). The results demonstrated the feasibility of such a large-scale survey and provided a realistic idea about the state-of-the-art of laboratory diagnosis in these countries: Besides some local specific problems, such as poor quality of water or the forced use of reagents and calibrators from different sources, there are general problems hindering an efficient process of 'harmonization' in laboratory medicine, namely, the high methodological dispersion especially in the case of enzymes and of some organic analytes. At the same time there is a potential necessity for more concentrated implementation of internal quality assessment into the routine work of laboratories.

Analytical specifications of reference methods compilation and critical discussion (from the members of the European EQA-Organizers Working Group B).

We present a compilation of published data for accuracy, precision, and measurement design for analytes that, currently, are of major interest for European reference laboratories. These data are compared with recent recommendations for performance of reference methods to be used within networks of European reference laboratories. In addition, we review the literature on reference methods and related topics.

Analytical quality specifications for reference methods and operating specifications for networks of reference laboratories. discussion paper from the members of the external quality assessment (EQA) Working Group B1) on target values in EQAS.

The aim of the Working Group was to describe guidelines for the establishment of networks of reference laboratories. The need for such networks to achieve an accuracy-based uniform measurement system with traceability of results of analytical systems/test-kits to the true value is outlined. Criteria for analytical quality specifications, which are related to the ultimate purpose of the reference method and thereby to the objectives of the networks, are emphasized. The group recommends the use of two models: one based on specifications for routine methods, which are dictated by the biological variations of the respective analytes, the second respecting the analytical state-of-the-art of reference methodology. Further, the group presents operating specifications for networks that guarantee the continuous performance of reference method measurements whilst maintaining a uniform and stable level of quality.

[Direct determination of inorganic phosphor in serum and urine utilizing Rhodamin B (author's transl)]. / Bestimmung von anorganischem Phosphor in biologischem Material mit einem einstufigen Reagens, enthaltend Rhodamin B

A micromethod is described for the spectrophotometric determination of inorganic phosphate in serum and urine utilizing Rhodamin B as a dye (phosphomolybdat-Rhodamin B complex), Brij 35, and polyvinylpyrrolidon as catalyst. The procedure does not involve deproteinization and yields a stable complex in 20 min. The linearity is constant up to at least 9 mg Pi per 100 ml. It is both accurate (r = 0.972 in serum, r = 0.989 in urine, recovery in urine 98%) and precise (vk = 1.16% in the series). Bilirubin up to 10 mg/100 ml and serum protein do not interfere with the method.