College of American Pathologists
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  Toxicology Information


Posted July 17, 2009

Toxicology Information

The College of American Pathologists (CAP) and the American Association of Clinical Chemistry (AACC) jointly developed the following fact sheet to provide patients and the public a better understanding of toxicology testing and to inform patients about precautions when taking multiple prescription medications.

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, including:

  • Clinical Toxicology – This 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. 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 patients who are taken to the 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.

  • Forensic toxicology – This type of testing is done postmortem (i.e., after a person dies). It 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 patients who are taken to the emergency department with a drug overdose.
  • While serum and urine are the primary patient specimens analyzed in clinical toxicology, postmortem 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, such as workplace drug testing, which screens for the "drugs of abuse" and athletic drug testing in sports programs, which look primarily for banned substances or performance enhancing drugs. These disciplines are strictly regulated and toxicologists working in these areas also have specific guidelines that 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), the 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.

Pathologists are physicians trained in laboratory medicine, anatomic or clinical 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 perform medical legal autopsies and conduct death investigations. Clinical chemists trained in forensic toxicology work closely with pathologists and medical examiners to decide what further testing needs to be performed and to evaluate the cause(s) of toxicity and/or death.

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.

What is the role of the pathologist in toxicology testing?
Pathologists request toxicology tests and interpret results to guide medical treatment, determine cause of death in forensic cases, and use toxicology testing to better understand drug interactions to help patients.

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:

  • Range of toxicologic specimens
  • Complexity of general unknown testing for the many illicit and therapeutic drugs as well as other toxic chemical agents
  • Importance of the forensic approach to confirmation testing by alternate methods on all initial positive drug findings
  • Challenge and interpretive value of quantification of drugs
  • Exchange of information between the toxicologist and the forensic pathologist during the investigation
  • 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.

What precautions should I take when taking prescription medications?
If you are taking multiple prescriptions, it is important to let your primary care physician know what medications you are taking - this includes over-the-counter medication and herbal supplements. Mixing prescription drugs can be dangerous to your health or even fatal.

Taking medications not prescribed to you can be harmful to your health. Patients should only take drugs prescribed to them and in the amount indicated.

About CAP
The College of American Pathologists is a medical society serving more than 17,000 physician members and the laboratory community throughout the world. It is the world's largest association composed exclusively of board certified pathologists and is widely considered the leader in laboratory quality assurance. The College is an advocate for high-quality and cost-effective medical care. For more information about the CAP, visit

About AACC
AACC is a leading professional society dedicated to improving healthcare through laboratory medicine. Its over 9,000 members are clinical laboratory professionals, physicians, research scientists, and others involved in developing tests and directing laboratory operations. AACC brings this community together with programs that advance knowledge, expertise, and innovation. For more information about the AACC, visit