False negative finding

Ensure that the analytical methodology gives reliable results in terms of identity (absence of false-positive findings) and of absence (no false-negative findings) of the analyte(s). This requires processing of concurrent analytical quality control samples. 

In order to conduct basic research and address the need for reagents and standards, several cell lines have been modified to express individual transporters. These can serve as a source of active protein to validate a chemical as a substrate or inhibitor, or as a source of protein to validate the specificity of an antibody. In order for this approach to be sufficiently robust to establish specificity (and to minimize false-negative findings), all of the key proteins need to be available and active in the system. However, as specific probes are being increasingly identified and developed, valuable mechanistic studies can be performed with the transporters and substrates/inhibitors that are currently available. 

In the diagnosis of intracranial stenosis, TOF-MRA is definitely superior to PC-MRA protocols. Oelerich et al. (1998) found a sensitivity of 87% for 3D TOF-MRA in intracranial stenoses. The correlation with DSA was 78%, and other authors found a correlation with MRA up to 88% (Dagirmanjian et al. 1995). While sensitivity is relatively high, false negative findings are rare, so that with sufficient examination quality, a good negative prediction is reached. 

There is recognized widespread concern about the possibility of both false positive and false negative findings at low ppm to low ppb concentration levels of the N-nitrosamines generally reported. Such artifacts could arise during sample preparation, extraction and/or subsequent chromatographic analysis (38). The... 

Kaufmann, A. and Butcher, P. 2006. Strategies to avoid false negative findings in residue analysis using liquid chromatography coupled to time-of-flight mass spectrometry. Rapid Commun. Mass Spectrom. 20 3566-3572. 

This preparation is routinely used at our institution in all patients referred for screening for colorectal cancer, change in bowel habit, iron deficiency anaemia, constipation, heme positive stool, etc. (see Chap. 2). Intravenous contrast is never used as the polyps may enhance and simulate tagged stool causing a false negative finding. 

A soft plaque at the initial stage of calcification may have an overall density of less than 400 HU. Should we now fill the vascular lumen with more than 400 HU of iodine contrast, some of the calcified structures adjacent to the lumen might be obscured and undiscernible from lumen territory on cross-sectional cuts (Fig. 16.3). This may potentially result in false-negative findings on coronary angiograms, which would constitute a worst-case scenario for the current clinical appHcation of the modahty. 

---