Drug screening with EMIT reagents: a quantitative approach to quality control

Area of Science:

• Clinical Chemistry
• Toxicology
• Analytical Chemistry

Background:

• Quantitative analysis of drugs of abuse is crucial for clinical and forensic toxicology.
• Immunoassay methods are widely used for drug screening, requiring validation for accuracy and precision.

Purpose of the Study:

• To assess the precision, linearity, accuracy, and stability of quantitative results for five drugs of abuse.
• To evaluate the performance of EMIT d.a.u. reagents on a Monarch 2000 analyzer with a nonlinear calibration algorithm.
• To determine the impact of calibration frequency on assay stability over a 30-day period.

Main Methods:

• Quantitative analysis of amphetamines, benzoylecgonine, opiates, phencyclidine, and THC-9-acid metabolite in control specimens.
• Utilized EMIT d.a.u. reagents (Syva Co.) and a Monarch 2000 analyzer.
• Employed a nonlinear interpolation curve-fitting algorithm for data analysis.

Main Results:

• Within-day and between-day coefficients of variation (CVs) were <5% for most drugs.
• THC-9-acid showed higher CVs (10-20%) and limited stability (2-3 days) without daily calibration.
• Daily calibration significantly improved control value stability and assay precision over 30 days.
• Mean control values near NIDA cutoff limits were within 10% of target values.

Conclusions:

• The EMIT d.a.u. assay with nonlinear calibration provides precise and accurate results for most tested drugs of abuse.
• THC-9-acid metabolite requires more frequent calibration (daily) for reliable quantitative results due to its limited stability.
• Daily calibration is recommended to maintain optimal precision and minimize drift in drug of abuse assays over time.