False positives endogenous

Other minor enzyme systems can be used such as betagalactosidase (5). This system works well however, it can lead to some false-positive problems resulting from endogenous enzymes that have a similar reactivity (d). Another enzyme not commonly used is glucose oxidase. A glucose oxidase system... 

Typically, the mass window is set for +/—10 mDa. The purpose of using a narrow mass window is to provide high selectivity for GSH conjugate detection and to exclude false positives from nominal mass endogenous components. 

These considerations show clearly that endogenous interpretive false positives are the main problem confronting urinalysis. It is, however, a problem with which hair analysis can provide considerable assistance, since passive exposure as a cause for a positive urinalysis result can be excluded by a positive hair analysis result. As indicated previously, this support is particularly critical in the case of opiates, where considerations of public safety demand that the numerous overturned urinalysis results be further investigated. 

The main issue in hair testing is the avoidance of exogenous interpretive false positives, i.e., positives caused by external contamination of hair by drugs present in the environment, e.g., smoke, powder. This type of false positive is not the major issue for urinalysis where endogenous interpretive false positives are the main concern. But, the effective avoidance by urinalysis of exogenous false positives due to specimen contamination in the laboratory depends critically on the exclusion of drugusing personnel, and this can best be achieved by evasion-proof hair analysis. However, when such false positives occur, or when urinalysis labs are unable to guarantee that they have taken effective measures to exclude such contamination, then very little can be done to remedy the problem. For, in contrast to hair, the collection of a new urine specimen identical to the first one is not possible. 

If one now adds to these safety features against exogenous false positives the ability to collect a second hair sample, safer endogenous cutoff levels, the trilevel reporting system (negative, contaminated, or positive), as well as the subversion-proof nature of the hair test, one can readily appreciate that hair analysis is a safer procedure than urinalysis. One also recognizes that hair analysis, unlilce urinalysis, is not a stand-alone test. 

Le Bizec et al. [64] demonstrated the detection of 19-norandrosterone and 19-noretiocholanolone in human urine subsequent to boar consumption using positive-ion LC-ESI-MS-MS. The detection of these steroids is generally used to confirm exogenous administration of 19-nortestosterone (nandrolone). However, a (false) positive result can be obtained from an athlete who ate pork meat. In a subsequent study [65], endogenous 19-norsteroids in boar meat were identified and quantified. 

Other benefits of polymer-based methods are also worth noting. Since this is a biotin-free system, the problems of false-positive staining due to endogenous biotin are overcome.Therefore, the efficiency of AR may be increased without the risk of evoking endogenous biotin activity. Furthermore, compared with three-step procedures, the technique is simpler, and assay time is decreased. Because of this, the risk of errors is reduced and reproducibility is increased. 

Diffuse, false positive cytoplasmic staining after HIER, due to endogenous biotin, may be eliminated with commercial... 

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