Clinical chemistry analytes detected

Immunoassays. Immunoassays (qv) maybe simply defined as analytical techniques that use antibodies or antibody-related reagents for selective deterrnination of sample components (94). These make up some of the most powerflil and widespread techniques used in clinical chemistry. The main advantages of immunoassays are high selectivity, low limits of detection, and adaptibiUty for use in detecting most compounds of clinical interest. Because of their high selectivity, immunoassays can often be used even for complex samples such as urine or blood, with Httle or no sample preparation. 

The majoiity of the various analyte measurements made in automated clinical chemistry analyzers involve optical techniques such as absorbance, reflectance, luminescence, and turbidimetric and nephelometric detection means. Some of these ate illustrated in Figure 3. The measurement of electrolytes such as sodium and potassium have generally been accomphshed by flame photometry or ion-selective electrode sensors (qv). However, the development of chromogenic ionophores permits these measurements to be done by absorbance photometry also. 

Fluorescence. The fluorescence detection technique is often used in clinical chemistry analyzers for analyte concentrations that are too low for the simpler absorbance method to be appHed. Fluorescence measurements can be categorized into steady-state and dynamic techniques. Included in the former are the conventional simultaneous excitation-emission method and fluorescence polarization. 

It should be noted that the term sensitivity sometimes may alternatively be used, namely in analytical chemistry and other disciplines. Frequently the term sensitivity is associated with detection limit or detection capability. This and other misuses are not recommended by IUPAC (Orange Book [1997, 2000]). In clinical chemistry and medicine another matter is denoted by sensitivity , namely the ability of a method to detect truly positive samples as positive (O Rangers and Condon [2000], cited according to Trullols et al. [2004]). However, this seems to be more a problem of trueness than of sensitivity. 

Clinical chemistry, particularly the determination of the biologically relevant electrolytes in physiological fluids, remains the key area of ISEs application [15], as billions of routine measurements with ISEs are performed each year all over the world [16], The concentration ranges for the most important physiological ions detectable in blood fluids with polymeric ISEs are shown in Table 4.1. Sensors for pH and for ionized calcium, potassium and sodium are approved by the International Federation of Clinical Chemistry (IFCC) and implemented into commercially available clinical analyzers [17], Moreover, magnesium, lithium, and chloride ions are also widely detected by corresponding ISEs in blood liquids, urine, hemodialysis solutions, and elsewhere. Sensors for the determination of physiologically relevant polyions (heparin and protamine), dissolved carbon dioxide, phosphates, and other blood analytes, intensively studied over the years, are on their way to replace less reliable and/or awkward analytical procedures for blood analysis (see below). 

General books [213-217], chapters [218], and reviews were published in the 1980s reporting the suitability of CL and BL in chemical analysis [219-222], the specific analytical applications of BL [223], the CL detection systems in the gas phase [224], in chromatography [225, 226], the use of different chemiluminescent tags in immunoassay, and applications in clinical chemistry [227-232] as well as the applications of CL reactions in biomedical analysis [233]. 

Albumin - [BLOOD, ARTIFICIAL] (Vol 4) -clinical assay for [AUTOMATED INSTRUMENTATION - CLINICAL CHEMISTRY] (Vol 3) -detection of [BIOPOLYMERS - ANALYTICAL TECHNIQUES] (Vol 4) -mineral nutrient carrier [MINERALNUTRIENTS] (Vol 16) -quimdme binding to [CARDIOVASCULAR AGENTS] (Vol 5) -role in pharmacokinetics [PHARMACODYNAMICS] (Vol 18) -sex hormone complex [HORMONES - SEX HORMONES] (Vol 13)... 

The majority of the various analyte measurements made in automated clinical chemistry analyzers involve optical techniques such as absorbance, reflectance, luminescence, and turbidimctric and nephelometric detection means. 

With the introduction of quality assurance in the diagnostic laboratory 56 years ago [6], a kind of educational and benchmarking process started forcing laboratories, national and international organizations, and the IVD industry to improve the methods applied in clinical laboratories. Comparison of the measurements of enzyme activity demonstrate that the analytical performance of the methods applied 30 years ago were far beyond the biological variation and most probably insufficient for medical needs. Interlaboratory comparisons show that with the new routine methods based on recommendations of the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) (Table 5) comparable results can be obtained irrespective of time and space and thus small individual variations can now be detected. Similar improvements in the analytical process in clinical laboratories can be reported generally for homogenous measurands. 

Ion-selective electrodes (ISEs) represent the current primary methodology in the quantification of S-Li [11-13], Moreover, ISE modules are parts of large and fully automated clinical chemistry analysers. In practice, the validation parameters are most often chosen in terms of judging the acceptability of the new measurement system for daily use. For this reason, the first approach was to study whether the detected imprecision fulfilled the desired analytical quality specifications. Secondly, proficiency testing (PT) results from past samples were of great value in predicting future bias. The identity of the three ISE methods was evaluated using patient samples. The analytical performance was checked after 6 months routine use. Without any exception, method validations always mean an extra economical burden. Therefore, the validation parameters chosen and processed have to be considered carefully. 

Figure 4-12 Design of amperometric enzyme electrode based on anodic detection of hydrogen peroxide generated from oxidase enzymatic reaction (e.g., glucose oxidase) (A), and expanded view of the sensing surface showing the different membranes and electrochemical process that yield the anodic current proportional to the substrate concentration in the sample (B). (From Meyerhoff N, New in vitro analytical approaches for clinical chemistry measurements in critical care. Clin Chem I990 36 I570.)...

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