Considerable interest has risen in the idea that oxidative stress is instrumental in the etiology of numerous human diseases. Oxidative stress can arise through the increased production of reactive oxygen species (ROS) and/or because of a deficiency of antioxidant defenses. Antioxidant deficiencies can develop as a result of decreased antioxidant intake (such as vitamins C and E), synthesis of enzymes (such as superoxide dismutase and glutathione peroxidase) or increased antioxidant utilization. Insufficient antioxidant enzyme synthesis may in turn be due to decreased micronutrient availability (such as selenium, magnese, copper and zinc). Of those diseases linked with oxidative stress, cardiovascular disease provides the strongest evidence for the protective role of antioxidants. A high consumption of fruit and vegetables, which are good sources of antioxidants, is associated with a lower coronary risk. More specifically, there is evidence of a reduced coronary risk in populations with high blood levels of the antioxidant nutrients, vitamins C and E. Evidence is also accumulating that diabetes, and microvascular complications associated with diabetes, involve oxidative stress and have compromised antioxidant status. In addition, patients who develop acute respiratory distress syndrome (ARDS) also exhibit clear evidence of oxidative stress. Definitive proof for active oxygen formation and oxidative cell damage being causative rather than a result of other underlying these pathologies remains elusive; however, evidence is sufficiently compelling to suggest that antioxidants are potential therapeutic agents in the above conditions.
Magnetic resonance spectroscopy is a powerful technique for the analysis of complex mixtures. Up to now, little of its potential in everyday clinical chemistry has been realized. An overview of the fundamentals, a discussion of the technology, and some outstanding examples of the clinical chemical research are presented. Clinical chemists are encouraged to seek out and apply this methodology to problems for which it is well suited.
Aging is the accumulation of changes that increase the risk of death. Aging changes can be attributed to development, genetic defects, the environment, disease, and the inborn aging process. The latter is the major risk factor for disease and death after age 28 in the developed countries. In these countries, average life expectancies at birth (ALE-B) now range from 76-79 years, 6-9 years less than the limit of about 85 years imposed by aging. Aging changes may be caused by free radical reactions. The extensive studies based on this possibility show promise of increasing the ALE-B to 85 years and beyond.
The presence of a serum and/or urinary monoclonal immunoglobulin (monoclonal component, MC), or its subunits, heavy and light chains produced by a B cell clone in serum and/or urine characterizes a wide group of conditions called monoclonal gammapathies (MG). In most instances, the MG is clinically silent, and remains so throughout life. However, the clone may be, or will become, clinically overt because of its proliferation (i.e., multiple myeloma and its variants) and/or because the MC produces organ damage (i.e., kidney failure, amyloidotic cardiomyopathy, etc.). The clinical laboratorian greatly contributes to the diagnosis and management of these conditions mainly through detection and quantitation of the monoclonal immunoglobulin, which represents an ideal tumor marker.
We give an overview of current methods for the detection of point mutations as well as small insertions and deletions in clinical diagnostics. For each method, the following characteristics are specified: (a) principle, (b) major modifications, (c) maximum fragment size that can be analyzed, (d) ratio and type of mutations that can be detected, (e) minimum ratio of mutant to wild-type alleles at which mutations can be detected, and (f) detection methods. Special attention is paid to the possibilities of quality assessment and the potential for standardization and automation.
A wide range of nongovernmental organizations are involved in laboratory quality assurance at the international level. These organizations include for-profit organizations such as Murex or Randox, nonprofit organizations such as the Institute for Standardization and Documentation in Medical Laboratories (INSTAND), national professional organizations such as the National Committee for Clinical Laboratory Standards (NCCLS), regional organizations such as the Asian Pacific and Latin American Federation of Clinical Biochemists and International organizations such as the IFCC and WHO. The Interaction and roles of such organizations are discussed.
Each year a vast number of biomedical articles and books are published and based on the articles reviews are written. Such reviews should be performed in a systematic manner. Systematic reviewing is a new discipline with its own methods for locating, appraising, and summarizing primary studies. Such methods have also been developed for studies on diagnostic test evaluations. It is important for the laboratory disciplines to engage in this work. IFCC has established a Committee for Systematic Reviewing in Laboratory Medicine. This committee will work to promote the understanding, the use and the performance of systematic reviewing.
Phosphate is an important component of all tissues and disorders of phosphate homeostasis are common in hospital populations. Hypophosphatemia, which is much more frequent than hyperphosphatemia, is commonly caused by infusion of carbohydrate or respiratory alkalosis. If hypophosphatemia is prolonged, severe consequences such as hemolysis, myopathy, and respiratory dysfunction may occur. In order to prevent these complications it is important to measure plasma phosphate concentration in a number of clinical situations. If severe hypophosphatemia is detected, phosphate supplements should be given to correct it.
Prostate-specific antigen (PSA) is the most important tumor marker for prostate cancer, although it is not a perfect marker as it is not cancer-specific. PSA, a member of the human kallikrein family, is present in two molecular forms in serum: free and complexed to protease inhibitors. PSA is now commonly measured on automated immunoassay systems employing monoclonal or polyclonal antibodies. Results from different assays can vary since some assays are not equimolar and react to the free and complexed forms differently. Utilization of the molecular forms of PSA is one approach to improve the sensitivity and specificity of the PSA assay. Patients with prostate cancer have a greater percentage of PSA bound to alpha1-antichymotripsin (ACT) than those without cancer. Measurement of the free to total PSA ratio in the diagnostic gray zone (usually 4-10 micrograms/liter of total PSA), where prostate cancer and benign prostatic hyperplasia (BPH) overlap, has been shown to eliminate between 16 and 79% of unnecessary biopsies. Free to total PSA cutoffs are influenced by the sensitivity and specificity values chosen, the reflex range for total PSA used, differences in free PSA assays, differences in populations studied, and factors such as total PSA concentrations, age, and prostate gland size. In addition to the molecular forms of PSA, age-specific reference ranges, rate of change of PSA concentrations (PSA velocity), ratio of serum PSA to prostate volume (PSA density), and neural network derived indices have been employed to improve the clinical utility of PSA measurements.
Immunoassay and other ligand assays have made a major impact on medical research and diagnosis since the first modern (radioisotopically-based) methods emerged. These ubiquitous microanalytic techniques are broadly classifiable as first generation (generally of "competitive" design, e.g., radioimmunoassay), and second generation (generally "noncompetitive," and relying on nonisotopic labels) these (often described as "ultrasensitive") being distinguished by dramatic improvements in sensitivity and performance time. A third generation is now in prospect (based on microarrays of antibody microspots) capable of ultrasensitive determination of hundreds of analytes in a drop of blood. Analogous technology (based on oligonucleotide arrays) is under intensive development for DNA analysis. Array technologies are likely to transform diagnostic medicine in the next decade.
Considerable advances have been made in our understanding of the genetics of primary immunodeficiencies over the last few years. The genetic defects underlying many forms of severe combined immunodeficiency, antibody deficiency, and neutrophil disorders are now known, raising the possibility of curative gene therapy for severe defects. These advances have also led to significant changes in our knowledge of basic mechanisms, not only of immunologic control but of cellular development and gene regulation.
The identification of the specific mutation causing an inherited disease in a patient is the framework for the development of a rationale for therapy and of DNA-based tests for screening relatives. We present here a review of the single-strand conformational polymorphism (SSCP) method, which allows DNA fragments that have been amplified with specific primers and PCR to be scanned rapidly for any sequence variation. The general principles of the method are described, as are the major factors that must be considered in developing an optimal SSCP strategy, namely length of the PCR fragment and the temperature of the gel run. Options for sample denaturing gel characteristics and detection of DNA fragments are discussed. In addition, several modifications are presented that have been developed for high-throughput mutational analysis. The application of these techniques to screen for mutations in the LDL receptor gene in patients with familial hypercholesterolemia are described.
In principle, flame photometry measures substance concentration, and ion-selective electrodes (ISEs) measure ion activity. However, the situation regarding the comparison of results from the two techniques when applied to blood plasma is complex. The problem can be approached experimentally from the point of view of calibration of ISEs with concentration calibrators, and similar procedures are adopted for commercial ISE-based clinical analyzers. Nevertheless, there is interest in the evaluation of single ion activities in blood plasma and solutions simulating its ionic composition. Solutions are proposed for calibrating ISEs for the determination of sodium, potassium, and calcium. It is recommended that the values for single ion activities derived from the Pitzer treatment of mixed electrolyte solutions be adopted, because, although this has some empirical features, it has a sounder theoretical basis than the previously used Stokes-Robinson-Bates hydration approach.
A number of reliable methods are currently available for the diagnosis of Helicobacter pylori infection. These diagnostic tests can be classified into invasive methods that require endoscopy and gastric biopsy, and noninvasive methods. Invasive methods include gastric mucosal biopsies at endoscopy for bacteriologic culture, histology, and the rapid urease test. Noninvasive methods include the urea breath test and serologic tests. Each of these diagnostic tests has its advantages and disadvantages. Histologic examination remains the gold standard for diagnosis. It can also detect coccoidal forms of the bacteria and be used to assess the severity of gastritis. Culture of H pylori should be performed if antibiotic sensitivity of the organism is required. A rapid urease test is the quickest test for H pylori status. The urea breath test detects urease activity in the entire stomach, thus eliminating the possibility of a sampling error, which occurs in random gastric biopsies. Serologic tests using either ELISA or latex-agglutination methods are excellent for diagnosis of H pylori infection, but not useful for monitoring effects of therapy. Recently, the polymerase chain reaction has been applied to fixed-tissue biopsies, as well as body secretions in the diagnosis of H pylori infection.
A number of reliable methods are currently available for the diagnosis of Helicobacter pylori infection. These diagnostic tests can be classified into invasive methods that require endoscopy and gastric biopsy, and noninvasive methods. Invasive methods include gastric mucosal biopsies at endoscopy for bacteriologic culture, histology, and the rapid urease test. Noninvasive methods include the urea breath test and serologic tests. Each of these diagnostic tests has its advantages and disadvantages. Histologic examination remains the gold standard for diagnosis. It can also detect coccoidal forms of the bacteria and be used to assess the severity of gastritis. Culture of H pylori should be performed if antibiotic sensitivity of the organism is required. A rapid urease test is the quickest test for H pylori status. The urea breath test detects urease activity in the entire stomach, thus eliminating the possibility of a sampling error, which occurs in random gastric biopsies. Serologic tests using either ELISA or latex-agglutination methods are excellent for diagnosis of H pylori infection, but not useful for monitoring effects of therapy. Recently, the polymerase chain reaction has been applied to fixed-tissue biopsies, as well as body secretions in the diagnosis of H pylori infection.
Laboratory and non-laboratory methods for assessing protein-energy nutritional status are reviewed. These are classified into methods for assessing adequacy of recent nutritional intake, methods for assessing whole body status, and tests which assist in the interpretation of these assessments. Each measurement is critically discussed in terms of the rationale for its use, the method of analysis, reference values, technical interference and limitations of methods, the effects of nutritional status and of other factors on the results, its overall usefulness in nutritional assessment, and its value relative to other methods. Non-laboratory tests, such as dietary assessment, indirect calorimetry, functional tests and the many methods available for assessment of body composition, including anthropometry, bioelectrical impedance and isotope and imaging techniques, are compared with the clinical chemistry tests in common use, such as nitrogen balance, plasma protein measurements and urinary markers of muscle metabolism. This review provides comprehensive and practical advice on the use and limitations of these tests in the assessment of protein-energy nutritional status of a group, or of an individual patient.
The objectives of the health reforms introduced in 1994 include universal coverage and cost containment. With these reforms, a new uniform for schedule and standards for laboratories have been introduced. The impact of these reforms is yet to be realized. It is predicted that with the imposition of new standards, many laboratories based in physicians' offices will disappear. Standards will also require more scientists and physicians trained in laboratory medicine.
Total quality management (TQM) of laboratory services is connected with a comprehensive system of quality assurance, which integrates quality development, quality maintenance, and quality improvement. TQM concentrates not only on analytic performance and organizational issues, including specimen collection, reporting, and interpretation of results, but focuses also on the benefits to society related to the use of specific laboratory tests in prevention, early detection, and therapy monitoring, as well as on outcome measures. A prerequisite to TQM are international and national standardization programs for the establishment of optimized and standardized methods, as well as for the development and evaluation of suitable reference materials. Reference materials that have been or are being prepared, calibrated, and certified by international and national reference institutions will certainly contribute to the harmonization of results, with different test systems in hemostaseology, improving their quality and value.
Belatedly, automation is being introduced into hemostasis laboratories. Now, new analytic systems are also available for less specialized laboratories. New tests have been added as knowledge of the mechanisms of coagulation increases. This article will review the new technologies in coagulation testing and their diagnostic applications.
