Setting cutoff concentrations for immunoassay screening of postmortem blood

Area of Science:

• Forensic Toxicology
• Analytical Chemistry
• Immunoassay Development

Background:

• Accurate drug abuse screening in postmortem toxicology is crucial for coroner's cases.
• Previous methods relied on double antibody radioimmunoassay (RIA), necessitating evaluation of newer techniques.
• Optimizing immunoassay cutoffs is key to ensuring reliable screening results.

Purpose of the Study:

• To establish optimal immunoassay cutoff concentrations for a coated tube RIA.
• To ensure the coated tube RIA performs equally to or better than the double antibody RIA.
• To validate screening results against GC/MS confirmation.

Main Methods:

• Evaluated 4-7 cutoff concentrations for opiates, amphetamines, cocaine, and barbiturates.
• Utilized 350 postmortem blood and liver homogenate specimens.
• Compared coated tube RIA results with GC/MS and GLC (NPD/FID) confirmed results.

Main Results:

• Selected cutoffs: 5 ng/mL morphine, 25 ng/mL methamphetamine, 500 ng/mL benzoylecgonine, 500 ng/mL secobarbital.
• Achieved high sensitivity and specificity for the coated tube RIA across drug classes.
• Demonstrated comparable or superior performance to the double antibody RIA for most drug classes.

Conclusions:

• The established cutoffs for the coated tube RIA provide reliable screening for drugs of abuse in postmortem samples.
• The coated tube RIA is a viable alternative to double antibody RIA for forensic toxicology screening.
• Optimized cutoffs enhance the accuracy and efficiency of postmortem drug testing.