False-positive Amphetamine Research Articles

Development and evaluation of an improved method for screening of amphetamines.

We developed a homogeneous immunoassay method to eliminate false-positive amphetamine results caused by cross-reactive substances, including over-the-counter allergy and cold medications. This method uses a neutralizing antibody that binds to amphetamines but does not bind to the labeled amphetamine conjugate used in the assay. The amount of neutralizing antibody is sufficient to reduce the assay signal resulting from authentic amphetamine and methamphetamine, but not the signal resulting from cross-reactants. This concept was implemented using the CEDIA DAU Amphetamines assay on Hitachi 747 and 717 clinical chemistry analyzers. Urine samples were tested using the standard, unmodified reagents in one channel and reagents containing the neutralizing antibody in a second channel. The difference in rate between the two tests was calculated by the analyzer; true-positive samples showed a significantly greater decrease in assay signal in response to neutralizing antibody as compared with false-positive samples. The neutralization method was evaluated in two studies using 448 samples that tested positive in the initial CEDIA DAU Amphetamines screening test. The samples were separated into categories of 154 true-positive samples and 294 false-positive samples based upon a secondary screen with the Abbott FPIA Amphetamines assay followed by gas chromatography-mass spectrometry (GC-MS) testing using the HHS (SAMHSA) cutoff criteria. The CEDIA neutralization test successfully identified all 154 of the GC-MS confirmed positive samples. The test successfully identified as false positive 251 out of the 294 (85.4%) samples that failed to confirm by GC-MS.

Application of the novel immunoassay TRIAGE to a rapid detection of antemortem drug abuse.

The applicability of the immunoassay TRIAGE (E. Merck, Darmstadt, Germany) as a simple and rapid assay for antemortem drug abuse was tested on 100 urine samples from forensic autopsies. The samples were also analyzed by fluorescence polarization immunoassay and by chromatographic methods. The confirmation rate of the TRIAGE results by chromatographic analysis was 92% for benzodiazepines, 95% for cannabinoids, 96% for cocaine, 100% for opiates and barbiturates, and 82% for amphetamines. Because the urine samples were taken from corpses, the latter finding can be explained by false-positive amphetamine results due to cross-reactivity of the antibodies used in current immunoassay technologies with phenylalkylamines, which are generated in postmortem decomposition processes. In fact, tyramine, a typical product of putrefaction, was identified by gas chromatography-mass spectrometry in 11 samples of false-positive amphetamine determinations. TRIAGE produces positive amphetamine results for samples containing tyramine in concentrations of more than 5 mg/L. The detection limit of the TRIAGE assay for 7-aminoflunitrazepam, the major urinary metabolite of flunitrazepam, is within the range of 0.5-1 mg/L.

Synthetic sweetener cyclamate as a potential source of false-positive amphetamine results in the TDx system

Synthetic sweetener cyclamate as a potential source of false-positive amphetamine results in the TDx system

False-positive urine amphetamine screen with ritodrine.

False-positive urine amphetamine screen with ritodrine.