Problems Associated with Clinical Chemistry Quality Control Materials

Fraser, Callum G.; Peake, M J

doi:10.3109/10408368009108726

Cited by 32 publications

(18 citation statements)

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“…As a rule, this is attained by freezing or by lyophilization of the sera. Frozen control ma terials produced in the laboratory itself have a number of advantages (e.g., costs, unifor mity, eliminated reconstitution) as compared with lyophilized products [2,3], Therefore, it is the goal to use these materials also for the quality control of determinations of enzyme activities [2], This fails, however, due to the insufficient stability of various enzymes [7], Also the investigations performed at lower temperatures concerning the stability of enzymes in human serum do not allow a reliable statement, also because only some enzymes were determined [10,14], This into account that a-amylase of the control serum Enzatrol could show a different behav iour in comparison to the a-amylase of hu man serum.…”

Section: Discussionmentioning

confidence: 99%

“…To ensure an effective quality control in clinical chemistry laboratories, the substance to be tested in control materials must simu late the corresponding components in the se rum of patients [3], Enzyme control materials often do not meet the basic requirement of 'similar behaviour'. This can be caused by the use of enzymes of different origin, e.g., from various animal species, and by the al teration of enzyme properties in control ma terials by means of manufacturing proce dures (e.g., lyophilization) [1].…”

Section: Introductionmentioning

confidence: 99%

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Long-Term Stability of Enzymes in Human Serum Stored in Liquid Nitrogen

Jung¹,

Bader²,

Grützmann³

1984

Enzyme

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We analyzed the stability of the enzymes α-amylase (EC 3.2.1.1), alkaline phosphatase (EC 3.1.3.1), alanine aminotransferase (EC 2.6.1.2), aspartate aminotransferase (EC 2.6.1.1), creatine kinase (EC 2.7.3.2), glutamate dehydrogenase (EC 1.4.1.3), γ-glutamyltransferase (EC 2.3.2.2) and lactate dehydrogenase (EC 1.1.1.27) of a human serum pool during storage in liquid nitrogen for a period of 10 months. Except amylase and creatine kinase, all enzymes were stable. Amylase increased in activity, creatine kinase activity decreased. Therefore, human serum stored at -196 °C can be used as satisfactory substitute for lyophilized enzyme control serum in internal quality control and stable enzyme material for optimization of methods.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Long-Term Stability of Enzymes in Human Serum Stored in Liquid Nitrogen

Jung¹,

Bader²,

Grützmann³

1984

Enzyme

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“…This subject has been described in detail by Fraser and Peake. 13 The hypothesis is certainly correct for glucose assays; in a study of components of biological variation performed by Williams, Harris and Widdowson, 14 the CV for paired serum samples from healthy subjects was 1·8% and for Iyophilised control material was 2·2%.…”

Section: Zx Numbcr Of Pairsmentioning

confidence: 99%

“…This performance standard has been maintained in 1984. 58 It is important to remember that caveats to these conclusions are that (i) these data were obtained generally from analyses of lyophilised materials which may differ from the human plasma specimens submitted to the laboratory for analysis 13 and (ii) it is possible to assay quality assurance sera under special conditions to gain apparently good performance.Y' 59…”

Section: Current Performance Vis-a-vis Goalsmentioning

confidence: 99%

Analytical Goals for Glucose Analyses

Fraser

1986

Ann Clin Biochem

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SUMMARY.Analytical goals may be defined as those standards of performance required to facilitate optimal patient care. Review of the considerable amount of published work on glucose analyses allows delineation of the following current goals:(a) For plasma glucose: within-laboratory between-batch imprecision -CV~2·2%; inaccuracy -no bias; linearity -I to 28 mrnol/L; detection limit -1 mrnol/L; turnaround time -30 min (in emergency situations). Moreover, each laboratory should develop goals for the many pre-analytical factors affecting glucose analyses. While the above goals are not always achieved in current practice, they are attainable and are worthy targets to strive to reach. The general principles discussed here for glucose analyses are applicable to other analytes of interest to the clinical biochemist.

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“…Use of this solution, as previously recommended," has significant advantages over the use of less stable solutions of NADH 9 or of quality control materials. The importance of optimisation of the standardisation procedure in improving the standard of performance of all types of assay has previously been stressed.…”

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confidence: 99%

The Effect of Instrument Variables on Calculation Factors for Standardisation of Colorimetric Analyses

1984

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SUMMARY.A number of colorimetric methods, particularly enzyme activity assays, are usually standardised using calculation factors based on the molar absorptivity of a principle reactant or product. Such methods are subject to long-term variation. The relationship between long-term variation in results and instrument variables affecting calculation factors has not been quantitated. In this study, we have shown that, on a centrifugal analyser having a within-run coefficient of variation of less than 1%, instrument variables affecting calculation factor alone could result in changes in results of up to 8·5% over 75 days. We therefore advocate daily use of a solution of potassium dichromate to monitor instrument variables that can independently affect calculation factors and within-run imprecision. This procedure is useful for maintaining long-term performance and for differentiating problems of instrumental or chemical origin.We have previously examined standardisation techniques for colorimetric analytical procedures!: 2 and have demonstrated experimentally that the mode of standardisationvariable, using a standard in each analytical batch, and constant, using a long-term relationship between concentration and absorbance-must be objectively selected for each method.In current practice, a number of analyses, particularly plasma or serum enzyme activity assays, are most often standardised using the constant calibration mode. For example, for enzyme activity assays, at a given temperature, the calculation involves: enzyme activity = calculation factor x absorbance change per minute.The absorbance change is corrected to a 1 em light path and the factor is derived from the formula:total reaction volume factor = b .. sample volume x umolar a sorptrvity Although this approach circumvents the very real difficulties of primary standardisation," a number of analyses, particularly enzyme activity assays, are often poorly performed at both inter-and intra-laboratory levels."There are a number of reasons for analytical problems; these have been reviewed by Lott.? Models for determining total system random error have been published;" 7 models for determining the effect of instrument variables on calculation factors have not.We therefore examined the reliability of calculation factors for analyses such as enzyme activity assays by making multiple daily absorbance measurements of a concentrated solution of a stable moiety, acid potassium dichromate, in order to monitor the principle variables of the above equation. Use of this solution, as previously recommended," has significant advantages over the use of less stable solutions of NADH 9 or of quality control materials. The importance of optimisation of the standardisation procedure in improving the standard of performance of all types of assay has previously been stressed. III This study has, therefore, the aim of assessing the relationship between long-term changes in results and the mode of standardisation. Materials and methods REAGENTApproximately 4 g of potassium dichromate...

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Problems Associated with Clinical Chemistry Quality Control Materials

Cited by 32 publications

References 103 publications

Long-Term Stability of Enzymes in Human Serum Stored in Liquid Nitrogen

Long-Term Stability of Enzymes in Human Serum Stored in Liquid Nitrogen

Analytical Goals for Glucose Analyses

The Effect of Instrument Variables on Calculation Factors for Standardisation of Colorimetric Analyses

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