Drug & Alcohol Forensic Review

"Positive" test results revealing the presence of commonly abused drugs, including cocaine, marijuana, and alcohol, are often critical pieces of evidence in accident investigations. Exponent employs a process for reviewing the validity and relevance of forensic drug evidence specific to the unique circumstances of each case. In our experience, it is clear that a positive drug test is not necessarily proof of intoxication or driver impairment.

A toxicologist who is retained to review the drug evidence must address two questions:


  • Is the drug test valid? 
  • Is the drug test relevant?

Bringing these questions into the consultant’s evaluation and testimony helps the judge and jury understand the role and value of the forensic drug-testing evidence in reaching their verdict. It also presents the evidence in a story format that can be followed easily, and can assist the court in reaching a logical conclusion. Many drug-testing laboratories are understaffed and receive a large number of samples for analysis every day. It is not uncommon to find that a positive test result is unreliable or invalid due to human error in procedure, or improper maintenance of testing equipment. Common questions regarding drug-test validity include the following:


  • What kind of sample was taken—blood, vitreous or urine?
  • When was it collected in relation to the said incident?
  • Were collection techniques properly executed to rule out contaminating factors?
  • Was the sample handled properly with regards to chain of custody?
  • Was it preserved/stored properly?
  • What type of laboratory analysis was performed, and does the laboratory have a formal Standard Operating Procedure (SOP) for that analytical method?
  • Did the technician follow the SOP?
  • Is the laboratory accredited?
  • Was the analytical equipment calibrated properly?
  • Was a blank sample run before the test sample?
  • What quality control/quality assurance procedures are in place at that laboratory?
  • Are there postmortem metabolic issues which must be factored into the analysis of the testing results?
  • Could the individual harbor genetic polymorphisms in metabolizing genes that affect the analysis?

Knowledge of the pharmacology of an abused substance is also important. Understanding the specific behavior of a drug in the body allows for proper interpretation of how quickly the drug is absorbed, how it is handled in the body, what metabolites are formed, how it produces its psychomotor and other toxic effects, and the relevant dose-response relationships. Exponent’s toxicology has broad expertise in evaluating the validity and relevance of drug evidence in criminal and civil investigations.

Professionals