American Association for Clinical Chemistry
Better health through laboratory medicine
Toxicology FAQs -July 2009
What is toxicology?

Toxicology is the study of drugs and toxins. Substances may be natural toxins (such as those associated with poisonous plants or animals), chemicals found in the environment (such as heavy metals like lead or cadmium), alcohols, or drugs (such as those used for therapeutic purposes or those used for illicit purposes such as heroin).   

What is meant by toxicology testing?

Toxicology testing falls into several categories. One category involves testing for drugs in a patient who comes to the emergency department in a hospital with signs and symptoms related to drug toxicity, i.e. clinical toxicology. In this case, laboratories may perform a “drugs of abuse screen” by a technology known as immunoassay on blood or urine obtained from a patient. The most commonly abused drugs such as amphetamines, barbiturates, benzodiazepines, cocaine, marijuana, methadone and opioids are screened first. In these patients that present to an emergency department for a drug overdose or toxicity, confirmation testing can be performed using more sophisticated instrumentation such as chromatography (gas, liquid or thin layer) alone or in combination with mass spectrometry if it is needed.

Another kind of toxicology testing is postmortem drug testing or forensic toxicology.  Forensic toxicology involves the application and interpretation of analytical toxicology for purposes of law. Initial drug screens may be similar to those used in clinical toxicology, but in general the number of drugs tested for and the sophistication of the analytical instrumentation is much greater in forensic drug testing. Postmortem cases require instrumentation that can detect drugs at a much lower limit than those used for specimens from a patient who presents to the emergency department with a drug overdose. While serum and urine are the primary patient specimens analyzed in clinical toxicology, post-mortem specimens submitted by the forensic pathologist for qualitative and quantitative measurement of drugs and poisons routinely include heart blood, peripheral blood, liver, brain, kidney, bile, gastric contents, vitreous humor, and urine.

There are additional types of toxicology testing, e.g. workplace drug testing which screens for the “drugs of abuse” and athletic drug testing in sports programs which look primarily for band substances or performance enhancing drugs. These disciplines are strictly regulated and toxicologists working in these areas also have specific guidelines which must be followed. 

Who conducts toxicology testing?

Toxicology testing is usually performed by trained and certified medical technologists (usually in the hospital clinical laboratory), or clinical chemists with a specialty in toxicology (this testing may take place in a special toxicology laboratory).  Clinical/forensic chemists have doctoral training and many are certified by either the American Board of Clinical Chemistry (for Toxicological Chemistry) or the American Board of Forensic Toxicology.  Some medical examiners offices also conduct toxicology testing that is associated with an autopsy. In addition, there are private laboratories, or reference laboratories that specialize in toxicological testing and perform tests that cannot be performed in these other laboratories.  All clinical or forensic laboratories must be accredited to ensure good quality results.  Examples of accrediting agencies are the College of American Pathologists (CAP), the Joint Commission (JC), American Board of Forensic Toxicology (ABFT) and various state health departments.

Who interprets toxicology testing?

Toxicology reports are interpreted by clinical toxicologists, clinical chemists or pathologists.  Clinical chemists trained in forensic toxicology work closely with pathologists and medical examiners (or coroners) to decide what further testing needs to be performed and to evaluate the cause(s) of toxicity and/or death.

Pathologists are physicians trained in laboratory medicine, anatomic pathology (or both) and are certified by the American Board of Pathology. Some clinical pathologists further specialize in the area of toxicology and forensic pathologists (medical examiners) perform medical legal autopsies and conduct death investigations. 

There are so many complexities of toxicology interpretation that a variety of health professionals who specialize in this field are required. Depending on the clinical setting,  drug concentrations may be interpreted differently depending on how fast (or slow) a patient metabolizes a drug (genetics), how old (or young) the patient is, whether they have been taking the drug a long (or short) period of time, or in cases of postmortem toxicology, how the drug distributes in the body. 

Why does toxicology testing take so long?

There are several reasons why forensic toxicology testing may take several weeks to complete. Some of these include 1) the range of toxicologic specimens, 2) the complexity of general unknown testing for the many illicit and therapeutic drugs as well as other toxic chemical agents, 3) the importance of the forensic approach to confirmation testing by alternate methods on all initial positive drug findings, 4) the challenge and interpretive value of quantification of drugs, 5) the exchange of information between the toxicologist and the forensic pathologist during the investigation, and 6) the extensive record keeping that is needed for forensic defensibility of the toxicology studies underlying a final report.  In addition, some tests may be beyond the scope of expertise in the initial laboratory and specimens will be referred to more specialized laboratories that can only perform those specific tests.  Forensic testing requires a “chain of custody” so that for each step, from collection of the specimen to the final report, there is documentation of where the specimen was and who handled it.

Toxicology reports are issued after a death investigation which would include information on any medications the deceased may have been taking or any drugs the deceased may have had access to. Death investigations take some time to gather all the information from the various individuals working on the case or who were involved with the deceased. Under certain circumstances, new information may become available and the toxicologist may have to test for an additional drug, or test another sample before the report is finalized.  Toxicology testing requires cooperative work among many professionals making communication and quality paramount.