Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (638 page)

   Minor metabolic pathways

   Low levels of allowable process impurities in pharmaceutical preparations

   Possible specimen adulteration

   
FORENSIC TOXICOLOGY

   Purpose

The discipline of clinical toxicology involves treating the poisoned patient, monitoring compliance with medications, or drug abstinence and monitoring drug concentrations in order to optimize dosing. The purpose is to treat patients. The discipline of forensic toxicology, however, involves the application of toxicology for legal purposes. Therefore, results from forensic toxicologic analysis may be used in courts of law. The level of proof is greater in forensic cases. As a result, specimen integrity is essential, and a chain of custody is utilized. Screening results are confirmed by a more specific and usually more sensitive technique. Forensic toxicology is broadly divided into three categories:

   Medicolegal death investigation

   Toxicologic analysis used to assist coroners and medical examiners in determining the cause and manner of death. Specimen types that may be included in this testing are blood from two sites, urine, vitreous humor, bile, cerebrospinal fluid, and tissues such as liver and brain.

   Drug testing

   Typically utilizing urine to test for drugs of abuse. Individuals may be subject to drug testing programs in the workplace, probation/parole (criminal justice system), sports, and in schools.

   Human performance

   Assessing the effects of drugs on human behavior to include operating a vehicle under the influence of ethanol and other drugs. Whole blood, serum/plasma, and urine are commonly used for this testing.

   Application

Although similar drugs may be detected and similar analytical techniques utilized in both clinical and forensic toxicology, the purpose of the testing is different, and interpretation of the findings is often dissimilar. Since laboratories may perform both types of testing, the practitioner should be aware of potential differences. One important difference is that immunoassay screening cutoff concentrations may vary between clinical and forensic applications. For example, clinical laboratories typically use a cutoff of 300 ng/mL for the qualitative screening opiate immunoassay. However, in the forensic application of workplace, drug testing 2,000 ng/mL is typically used. If a laboratory is conducting testing under the national laboratory certification program, utilized for testing federal employees, it is mandated by law to use this cutoff. However, a cutoff of 2,000 ng/mL for opiates is inappropriate for clinical applications due to the potential for significant false-negative results. Table
14-2
summarizes the screening and confirmation cutoff concentrations for laboratories accredited through the U.S. Department of Health and Human Services.