Toxicology

The interpretation of results can often be the most difficult job of the toxicologist. The analyst must understand the effects of a particular substance, what possible interactions it may have with other drugs or natural disease processes, and an understanding of what happens to toxins in the body over a period of time.

Coroners and medical examiners are responsible for determining the cause and manner of death, and they use all aspects of the case to do so, including circumstances, autopsy findings, crime scene details and any information from laboratory testing. With regard to toxicology, they need to be aware that unusual test distortions can occur that affect the interpretation of blood concentration. Biological samples can be unstable and can change or further degrade after they are collected for testing. Factors that can alter readings of drug concentration include quality of specimen due to decomposition, redistribution of drugs from other tissues, contamination or degradation of the drug after death. The effects of the concentration vary from person to person, and all factors must be considered when determining whether a substance found in the system can be identified as causing or contributing to behavioural changes or death.

Other limitations to toxicology for death investigations include the availability of specimens and the range of tests that can be conducted. If a death was not initially considered to be suspicious, an autopsy may not be performed. Even if the post-mortem examination occurs, appropriate samples are not always collected (and bodies may be quickly cremated or buried following this autopsy). As discussed above, there is almost an unlimited number of tests that can be conducted, but there may not be time, funds or the ability to perform these tests in many post-mortem labs. Also, many drugs or other toxins can move from one area of the body to other areas in a process known as post-mortem redistribution. Death trauma can change post-mortem levels so that test results are no longer clearly associated with levels before death. Even emergency or terminal life-saving procedures can add and change the ability to properly interpret results. These limitations can all be made more difficult if insufficient time is available for proper communications between the lab, pathologists and other investigators involved.

To ensure the most accurate analysis of evidence, the management of forensic laboratories puts in place policies and procedures that govern facilities and equipment, methods and procedures, and analyst qualifications and training. Depending on the state in which it operates, a crime laboratory may be required to achieve accreditation to verify that it meets quality standards. There are two internationally recognized accrediting programs in the U.S. focused on forensic laboratories: The American Society of Crime Laboratory Directors Laboratory Accreditation Board and ANSI-ASQ National Accreditation Board / FQS.

In disciplines such as toxicology, quality control is achieved through confirmation testing, technical review and verification of conclusions. As discussed above, the Scientific Working Group on Toxicology (SWGTOX) publishes methodology validation standards and guides for professional conduct. In addition, specific laboratory accreditation is offered by the American Board of Forensic Toxicology (ABFT), which uses peer-based consensus standards developed by the Society of Forensic Toxicologists (SOFT) and the Toxicology Section of the American Academy of Forensic Sciences (AAFS) to guide QA and QC in post-mortem examinations. ABFT (and SOFT-AAFS) standards are subject to international harmonization efforts with many other societies, and have long supported legal actions in death investigations.

The analysis report may contain a variety of information depending on the type of testing requested. For example, a report for a court file may need to be broader than for a negative drug test in drug abuse monitoring. The report should contain a list of the specimens analyzed and the tests performed on them. The methods used for the testing should be clearly stated and include information regarding the reliability of the test, for example, whether a confirmatory test could be done and if not, clarify the limitations of the information presented.

The final results must be clearly stated and characterized by the corresponding statistical degree of certainty. Medicolegal case investigations are confidential in nature and every precaution should be taken to ensure that information is released only to properly authorized personnel. Each laboratory must have its own policy for the retention and release of information.

Obviously, post-mortem breath tests are not possible, but breath alcohol tests are a screening tool that allows police officers, corrections officials, civil accident investigators and others to determine a course of action with regard to a person who appears to be intoxicated. Breath analyzers do not directly measure blood alcohol content or concentration, which requires the analysis of a blood sample. However, the technologies involved and the consistent relationship between the alcohol in one’s breath and the blood level allow results from these breath alcohol tests to be used regularly in legal proceedings. These non-invasive breath tests are not able to identify other potential causes of observed behavior, as blood testing may be able to do.

Toxicology results by themselves are no more than numbers; the final interpretation of post-mortem test results should only be reached after all of the factors in a case have been drawn together. These factors can include (but are not limited to) the histological evidence, the autopsy findings, the contribution of natural disease, the known circumstances of the case and the medical history of the deceased. It is ultimately the pathologist who assigns and officially reports the investigative determination as to the cause and manner of death.