Artifact markers

Two rules have been kept in mind when thinking about samples for biomarker discovery and primary validation. These rules are designed to reduce the complexity of discovery experiments by reducing the number of artifact and false markers that are the result of poor sample collection and handling processes, which often contribute to problems in statistical data analysis. These artifact markers can also mask real biomarkers and cause them to be ignored or missed in the early stages of the project. 

Successful flow cytometric analysis depends on adequate sample preparation (see Chapters 30-31), appropriate selection of probes or markers (see Subheading 2.), instrumentation, and data display and analysis. Each of these areas is interrelated and requires adequate attention to avoid the introduction of artifacts and misinterpretation of results. Flow cytometers tend to be excessively complicated and require a skilled operator for alignment and calibration, though manufacturers are introducing more compact, user-friendly data acquisition and image processing systems. 

One example is the known interference by reducing compounds that affect the chemical conversion of substrate to a colored indicator. This is especially true for the tetrazolium assays (Ulukaya, Colakogullari, and Wood 2004 Chakrabarti et al. 2000 Pagliacci et al. 1993 Collier and Pritsos 2003). The growing list of interfering compounds includes ascorbic acid and sulfhydryl reagents such as glutathione, coenzyme A, dithiothreitol, etc. Similar interferences by compounds that affect the oxidation and reduction chemistry of cells are likely to cause artifacts with the resazurin reduction assay. Assays that measure markers of metabolism also can be influenced by the pH of the culture medium and other factors that may stimulate or stress the metabolic rates of cells. 

In the UVB study we also measured malondialdehyde, a marker of lipid peroxidation, but were unable to detect any increase in response to UV light, in contrast to other reports. There are a number of possible explanations. In our experiment, a-tocopherol levels remained high after irradiation, and it is known that lipid peroxidation does not begin in in vitro membrane systems until a-tocopherol is completely depleted [29], Several studies have shown a time lag of one to several hours after irradiation to occur before a measurable increase in cutaneous lipid peroxidation can be detected [26-28] since skin was processed immediately in our experiments, lipid peroxidation may not have reached detectable limits. Finally, the TBARS assay for malondialdehyde is notoriously fraught with artifact and has a relatively high background [30], and noise levels may simply have been too high to detect peroxidation. Results... 

Immunohistochemically, the fusiform and pleomorphic cells of STCs express vimentin. Labeling for keratin and EMA is also seen, but it may be quite focal (Fig. 11.34). This finding opens the door to the possibility that a small biopsy specimen could fail to demonstrate any epithelial markers because of sampling artifact. 

Sampling. Water samples were collected in gallon glass jugs with teflon-lined stoppers. The jugs had been previously cleaned and silanized with dimethyldichlorosilane and were extracted to check for residues or artifacts of the marker compound prior to use. 

Concentrations of the marker compound (Figure 10) found during the high water table conditions for these three sites discussed above did not appear to correlate with extract color. The marker compound analytical data, however, contain uncertainty due to apparent chromatographic artifacts. The presence of colored compounds in the extractant, however, does provide an independent assessment of the possible interconnection between surface water and groundwater in this locale. The fact that the color patterns of the two houses compared were different also demonstrates potentially different pathways of flow that are reaching these two houses despite the close proximity of their wells. 

Due to the application of highly specific markers, i.e., monoclonal antibodies, the possible experimental artifacts are negligible. One problem when detecting the NPCs in the nuclear envelope are certainly those NPCs that are not yet assembled in the nuclear membrane, but are found, for example, in the annulate lamellae. Due to the high resolution in the axial direction, it will in most cases be possible to differentiate them from the nuclear envelope due to a different z position, but it cannot be excluded that some of the detected NPCs are not located in the nuclear envelope. 

Vd Defenses against loss of continuity of care include cognitive artifacts. These artifacts are intended to bridge the gap they also serve as markers that researchers can use to discover gaps. 

Fig. 19.5 Ventricular AutoCapture Threshold test performed with the Model 3510 Programmer at the time of a routine follow-up visit. The higher output back-up pulse is identified by the second V output marker and the much larger stimulus artifact following each loss of capture associated with the primary output pulse. During the test with the programmer, the delivered voltage associated with each pulse is also reported. The measured up-threshold is 0.625 V at a 0.4 ms pulse duration in a system that had been implanted 3 months earlier. Based on this result, the automatic pulse amplitude is set to 0.875 V by the AutoCapture algorithm.

Nonmedical uses of radioisotopes include (1) tracers in chemical reactions, (2) boundary markers between liquids in pipelines, (3) tracers to detect leaks, (4) metal-wear indicators, and (5) thickness indicators for foils and sheet metal. An especially interesting application is the determination of the ages of artifacts and rocks. 

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