Standards in clinical chemistry

The sera used as control samples and standards in clinical chemistry should remain stable over relatively long periods of time if they are to be useful and provide reliable results. 

Wll. Wootton, I. D. P., Standardization in clinical chemistry. Clin. Chem. 3, 401-405... 

The basic aim of PEC applications in clinical chemistry, apart from the recovery of standards of endogenous substances, consists of structural identification of isolated (without further separation) substances of relatively high purity. Therefore, the majority of works devoted to this topic pertain to semipreparative separation. Obtaining low amounts of analytes, achieved by coupling TEC with modem... 

Ingamells CO, PiTARD FF (1986) Applied Geochemical Analysis, pp L-84.Wiley, New York. International Federation of Clinical Chemistry (IFCC) (1978) Expert Panel on Nomenclature and Principles of Quality Control in Clinical Chemistry. Clin Chim Acta 83 L89F-202F. International Organization for Standardization (ISO) (1993) Guide to the expression of uncertainty. Geneva. 

In our opinion, investigations in the field of physiological and pathological peptiduria appear to have a very brilliant future. Further methodological advances, primarily in the development of uniform and standardized procedures making the results of different laboratories comparable, are, however, necessary before this trend of research gains an established position in clinical chemistry. 

In clinical chemistry, interpretation of the data can be quite simple or complex. In the case of MS/MS applications pertaining to a single analyte, all that is needed is the intensity value from the mass of a peak of interest and its internal standard. Viewing of a spectrum is not necessary. For profile methods such as full-scan acylcarni-tines, amino acids, or other compound families, the interpretation is more complex. With multiple related components, calculation of the concentration of many key metabolites is required. The system generally has multiple internal standards, external standards, or both. In addition to the concentration calculations, examination of a profile is often best achieved by viewing the spectra together with the quantitative information. 

The application of GC for use in the clinical laboratory is relatively new, due possibly to the shortage of qualified personnel to perfect and standardize GC as a routine clinical laboratory procedure. This occurred, even though highly sensitive and specific methodology of GC was available for many determinations. The methods presented in this chapter are taken from current literature and from the authors laboratory. Although the methods presented are not the only ones used in clinical chemistry, in the authors opinion they are the simplest and most reliable. 

Sieg A, Guy RH, Delgado-Charro MB. Noninvasive glucose monitoring by reverse iontophoresis in vivo application of the internal standard concept. Clinical Chemistry 2004, 50, 1383-1390. 

Steroids hormones in clinical chemistry Comparison of RIA, GC-MS/MS and LC-MS/ MS in steroid analysis role of LC-MS/MS in metabolomics, e.g., quantitative bioanalysis, identifying and profiling biomarkers standardization of MS assavs. [14]... 

Estrogens in clinical chemistry RIA, GC-MS/MS, and LC-MS/MS analyses of estrogens in serum and plasma isotope internal standard sample derivatization ionization modes and sensitivities of GC-MS/MS and LC-MS/MS. [4]... 

IFCC (1976). Internationa] Federation of Clinical Chemistry. Committee on standards expert panel on nomenclature and principles of quality control in clinical chemistry. Provisional recommendations on quality control in clinical chemistry, Part 1 General principles and technolgoy. Clin. Chem. 22, 532-540. 

This review is written for the clinical chemist who wishes to understand the principles of the main classes of instruments, their relative merits and applications, and the types likely to be important in the future. Equipment used for data processing, in vivo analysis, cell counting and morphology is excluded. Some instruments described in standard textbooks [e.g., (S15, W18)] have been omitted either because they have not developed significantly in recent years (e.g., nephelometers, refractometers) or because they have found little application in clinical chemistry (e.g., thermal analyzers). 

The quantitation of enzymes and substrates has long been of critical importance in clinical chemistry, since metabolic levels of a variety of species are known to be associated with certain disease states. Enzymatic methods may be used in complex matrices, such as serum or urine, due to the high selectivity of enzymes for their natural substrates. Because of this selectivity, enzymatic assays are also used in chemical and biochemical research. This chapter considers quantitative experimental methods, the biochemical species that is being measured, how the measurement is made, and how experimental data relate to concentration. This chapter assumes familiarity with the principles of spectroscopic (absorbance, fluorescence, chemi-and bioluminescence, nephelometry, and turbidimetry), electrochemical (poten-tiometry and amperometry), calorimetry, and radiochemical methods. For an excellent coverage of these topics, the student is referred to Daniel C. Harris, Quantitative Chemical Analysis (6th ed.). In addition, statistical terms and methods, such as detection limit, signal-to-noise ratio (S/N), sensitivity, relative standard deviation (RSD), and linear regression are assumed familiar Chapter 16 in this volume discusses statistical parameters. 

The necessary sample sizes for a series of standard method comparison situations in clinical chemistry have been tabulated (Tables 14-13 and 14-14). A Type I error (significance level) of 5% and a power of 90% have been assumed. Table 14-13 concerns the situation with constant SDs over the analytical measurement range, and Table 14-14 covers cases with proportional SDs. 

Most of the methods in use in clinical chemistry laboratories involve colorimetric analysis in fewer instances volumetric or gravimetric procedures are still retained. It is not the purpose of this review to enter into a discussion of the errors inherent in colorimetric, volumetric, and gravimetric analysis as such for a treatment of this subject the reader is referred to standard works on chemical analysis (e.g., V3). Instead, the review will be confined to those sources of error that are particularly likely to affect the work of a clinical laboratory. These errors arise mainly from the need to perform many analyses on large numbers of samples with a variable degree of urgency, and from the fact that most of these analyses have to be conducted on plasma or semm, which are viscous protein-rich fluids available only in restricted quantities (M12). 

Some surveys (e.g., F2, G4, WIO) included an assessment of the precision of each laboratory s work by distributing specimens with interrelated compositions or else duplicate samples, and the results of these comparisons showed that individual laboratories could compare the content of two solutions for the substances under evaluation more accurately than they could determine the absolute value of the particular constituent. This led Wootton (WIO) to state the very important conclusion that estimations in clinical chemistry laboratories should whenever possible be made by comparing an unknown with a standard solution, since such comparisons would reveal some errors which could otherwise pass undetected for a long time. This need to incorporate both standards and controls into routine use will be reconsidered later (Section 3.1.1). 

The results of most investigations performed in clinical chemistry laboratories are expressed in quantitative terms, and the characteristics of the methods adopted by different laboratories can therefore be assessed according to the standard criteria of quantitative chemical analysis. In such an assessment, definitions of terminology are important, and this section defines and discusses the following terms used frequently in this review ... 

This review will be more concerned with the determination and maintenance of standards of precision, particularly of reproducibility, than with the assessment of accuracy and specificity of methods in clinical chemistry. This is because accuracy and specificity can be determined in a laboratory in advance of introducing a method, and the limitations of each method in these respects defined and allowed for, whereas the precision obtained for the same method may differ markedly from time to time in one laboratory and from one laboratory to another. The trials of interlaboratory accuracy (Section 1.2) have not so far been able to distinguish fully between inaccuracy and imprecision in the performance of individual laboratories for the chemical determinations under evaluation. Imprecision, however, has probably been the main factor underlying the disturbing findings revealed by these trials, and the emphasis placed in this review upon the search for improved precision and its subsequent maintenance is justified by the fact that most of the work in clinical... 

Standard substances in clinical chemistry include primary standards, which can be obtained sufficiently pure to be used for the preparation of solutions by weighing or by reference to other definable physical characteristics (e.g., constant-boiling hydrochloric acid). Primary standard chemicals are available for acid-base reactions, precipitation reactions, oxidation-reduction reactions, etc. (V3), and are used in these various categories of analytical determination to validate the preparation of solutions of other chemical substances which cannot be obtained in a form suitable to meet the criteria demanded for a primary standard. Following their calibration in terms of a primary standard, these other chemieals can act as secondary standards. 

Standards should be used regularly in all clinical chemistry procedures to check the performance of reagents, the calibration of photometers, etc., and all quantitative results in clinical chemistry are calculated with respect to the performance of a standard (primary or secondary) preparation of the material under test, or of a closely similar material (e.g., dehydroepiandrosterone for group steroid assays) if the exactly corresponding standard material cannot be made available as a pure compound. 

In clinical chemistry, the closely controlled reaction conditions of quantitative inorganic and organic chemistry cannot always be obtained, since estimations have to be performed on complex mixtures. This means that both simple aqueous and protein-containing standards have to be considered, and the criteria adopted when choosing a standard for use in clinical chemistry may be unable to meet the criteria of primary standards used in other branches of quantitative chemistry. For some determinations, the accuracy of a method cannot be established at present since pure materials for standardization are not yet available the best examples of such methods are provided by determinations of enzyme activity in serum, but suitable control preparations exist for monitoring the precision of these assays (e.g., H8). 

Standard materials used in clinical chemistry include the following ... 

The control materials used in clinical chemistry include simple aqueous solutions of single compounds or mixtures of compounds (e.g., W13), and a wide variety of commercial protein-containing preparations (B6). For analyses of plasma or serum, protein-containing controls should be included among the specimens analyzed and these samples will be referred to as control sera. Under certain conditions, control sera can be used instead as standard preparations, and for some purposes there is no satisfactory alternative to standard sera for this (Sections 3.1.1.1 and 3.1.1.3). 

I.I.I. Biological Materials Used as Standards. For some analyses in clinical chemistry, pooled collections of serum or urine offer the only readily available standard materials, and for this purpose their content of these substances is first determined as accurately as possible. The composition of the biological material to be used as a standard is obtained by means of reference methods, but practical considerations thereafter prevent the daily checking of the standard serum, urine, etc., against these reference procedures. For the monitoring of reagent and instru-... 

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