False-negative results

Sensitive to toxins, in this case means that the assay presents no false negative results. Primary hepatocytes can elucidate hepatotoxins, and mouse neuroblastoma cells can elucidate sodium channel-blocking neurotoxins therefore these assays can be used to screen for the appropriate toxins. 

Drugs can also Interfere with laboratory results by negating certain nonspecific oxidation and reduction reactions essential for the chemical assay. Penicillin, streptomycin and ascorbic acid are known to react with cupric Ion thus, false positive results for glucose may occur If a copper reduction method Is used. If the specific enzymatic glucose-oxidase method Is employed, ascorbic acid can cause a false negative result by preventing the oxidation of a specific chromogen In the reaction. 

The file Is used routinely In the laboratory at the National Institutes of Health In an attempt to explain abnormal test results The resident physicians affiliated with the Clinical Chemistry Service discuss the results with the patient-care physicians and determine If the results were due to the patient s clinical state or to a drug effect This close monitoring of test results has led to recognition of deficiencies In what Is believed are specific enzymatic procedures for the measurement of glucose and uric acid Likewise, the gualac procedure for occult blood In feces was found to yield false negative results under certain circumstances This has prompted the development of a more specific procedure (Jaffe et al unpublished) ... 

Many diseases, including anthrax, are most effectively treated before actual manifestation of the symptoms is observed. Presently a presumptive identification of Bacillus anthracis can be made in about 3 hours however, if a full laboratory response network (LRN) confirmation procedure is utilized, the theoretical time increases substantially to approximately 48 hours. During the recent anthrax cases 72 to 96 hours were common to complete the entire LRN protocol. In the meantime antibiotics were administered as a precaution based on the presumptive results to individuals thought to be exposed to B. anthracis spores or with anthrax symptoms. The mass administering of antibiotics from a cost standpoint, as well as from medical prudence to prevent the rise of antibiotic-resistant strains, is not the optimal answer to the anthrax infection problem. Therefore it is important that early tests be rapid and reliable with a minimum number of false positive and false negative results. 

For tests designed to detect the presence or absence of an analyte, the threshold concentration that can be detected can be determined from replicate measurements over a range of concentrations. These data can be used to establish at what concentration a cut-off point can be drawn between reliable detection and non-detection. At each concentration level, it may be necessary to measure approximately ten replicates. The cut-off point depends on the number of false negative results that can be tolerated. It can be seen from Table 4.7 that for the given example the positive identification of the analyte is not reliable below 100 xg g-1. 

In sum, it seems plausible that L-mode may be prone to false negative results that is, it may overlook taxonicity. Consequently, we recommend applying this technique with caution and weighting the results of L-mode less heavily than the findings of more established procedures. It is important... 

Matrix effect is a phrase normally used to describe the effect of some portion of a sample matrix that causes erroneous assay results if care is not taken to avoid the problem or correct for it by some mechanism. The most common matrix effects are those that result in ion suppression and subsequent false negative results. Ion enhancement may lead to false positive results.126 127 Several reports about matrix effects include suggestions on what can cause them and how to avoid them.126-147 While various ways to detect matrix effects have been reported, Matuszewski et al.140 described a clear way to measure the matrix effect (ME) for an analyte, recovery (RE) from the extraction procedure, and overall process efficiency (PE) of a procedure. Their method is to prepare three sets of samples and assay them using the planned HPLC/MS/MS method. The first set is the neat solution standards diluted into the mobile phase before injection to obtain the A results. The second set is the analyte spiked into the blank plasma extract (after extraction) to obtain the B results. The third set is the analyte spiked into the blank plasma before the extraction step (C results) these samples are extracted and assayed along with the two other sets. The three data sets allow for the following calculations ... 

The study then examines whether this is true. The amount of data needed to prove a difference between the samples depends on the size of the difference that is to be detected. Enough data must be collected to minimize the risk of a false-positive or false-negative result. This is determined by a power calculation. 

Acceptable power is 80-90%, which equates to a / value of 10-20%. In effect, this means a 10-20% chance of a false-negative result. 

No exogenous vitamin C should be ingested for 48 to 72 hours before amine-dependent stool occult blood tests are conducted because possible false-negative results may occur. 

Thyroid 1 uptake may be decreased. False-negative results with the nitroblue-tetrazolium test for bacterial infection. Dexamethasone, given for cerebral edema, may alter the results of a brain scan (decreased uptake of radioactive material). 

Be sure to know the transfection efficiency. Poorly transfected cells could generate false-negative results. Set up a priori the optimal condition of transfection with a reporter gene. 

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