Development and evaluation of an improved method for screening of amphetamines

Area of Science:

• Clinical Chemistry
• Immunochemistry
• Forensic Toxicology

Background:

• False-positive results in amphetamine immunoassays are often caused by cross-reactivity with common over-the-counter medications.
• Accurate differentiation between true and false positives is crucial for reliable drug screening.

Purpose of the Study:

• To develop and evaluate a homogeneous immunoassay method to eliminate false-positive amphetamine results.
• To improve the specificity of amphetamine screening assays by distinguishing true positives from cross-reactants.

Main Methods:

• A neutralizing antibody was incorporated into the CEDIA DAU Amphetamines assay to selectively reduce signals from authentic amphetamines.
• The modified assay was tested on clinical chemistry analyzers (Hitachi 747 and 717) using urine samples.
• Results were compared between standard and neutralized assay channels to identify true positives based on signal reduction.

Main Results:

• The neutralization method correctly identified all 154 true-positive amphetamine samples confirmed by GC-MS.
• The assay successfully identified 85.4% (251 out of 294) of false-positive samples that did not confirm by GC-MS.
• A significant difference in signal reduction between true and false positives was observed.

Conclusions:

• The developed homogeneous immunoassay with a neutralizing antibody effectively eliminates false-positive amphetamine results.
• This method enhances the specificity of amphetamine screening, reducing interference from cross-reactive substances.
• The neutralization technique offers a reliable solution for improving the accuracy of drug testing assays.