What is a toxicology screen?

Toxicology screening is a diagnostic test that detects the presence and amount of illegal drugs, alcohol and various other potentially harmful substances in the body. Its primary goal is to detect substances that may harm a person's health and behavior. Toxicology screening is a vital diagnostic tool in healthcare, forensic toxicology and human resources (HR) operations.

What is a toxicology screening test used for?

Here are examples from the wide range of applications for toxicology screening

• Identifying overdoses: Clinicians can assess whether a person took too much of a drug accidentally or recreationally.
• Monitoring substance abuse: Toxicology tests can be implemented to monitor substance abuse in clinical settings, rehabilitation programs, workplaces and sports.
• Diagnosing poisoning or toxic exposure (poison screening): Tests can reveal overexposure to industrial toxins, heavy metals or poisonous gases.
• Evaluating altered mental states, seizures or unconsciousness: Toxicology of drugs or other substances in a person's body may contribute to their altered mental states, coma-induction or unusual neurological symptoms.
• Alcohol screening for alcohol use disorders or withdrawal symptoms: Alcohol testing is often used to monitor the alcohol levels in a person due to alcohol poisoning or chronic use. Withdrawal during recovery can also be tracked by measuring alcohol levels.
• Toxicology testing for forensic investigations: Toxicology tests can help reveal the role of drugs or toxins in unusual behavior, injury and death.
• Preclinical toxicology tests can be performed during cell line development and drug screening to assess potential drug toxicity to the heart, brain and liver.

Types of toxicology tests

Screening the blood and the urine are the two most common ways to detect hazardous substances, although other tests can be used for different applications.

Blood toxicology tests

Because blood circulates throughout the body, its content often gives insights into the body's biochemical activities. Blood toxicology tests provide a detailed snapshot of the toxic or excessive content in the blood.

Once a blood sample is collected from a patient, it is sent to the laboratory for various screening tests. A rapid immunoassay (e.g., ELISA) is conducted to quantify antibody binding to drugs and toxins. Confirmatory tests, such as gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-mass spectrometry (LC-MS), are carried out for more precise quantification. Together, these tests can identify the original compound and its metabolites processed by the liver. Moreover, concentration levels can assist clinicians in determining the time of ingestion and the impact of the dose on the body.

In medical emergencies, blood tests are commonly used to evaluate unconscious patients, suspected poisoning or seizures. They also play a crucial role in post-mortem analysis to identify the cause of death.

Featured Product

Urine toxicology tests

Urine toxicology tests are often preferred for routine and long-term toxicology screening due to their cost-effectiveness and non-invasive nature.

Urine tests have a broader detection window than blood tests. Certain substances and metabolites may remain detectable in the urine for days or weeks after ingestion. For instance, cannabis content may show up in the urine for months after the most recent use.¹ Thus, these tests are invaluable for determining chronic use of drugs or substances that may affect a person's behavior and performance. Urine toxicology is frequently used during the hiring process or to identify possible contributing factors to workplace accidents or misconduct.

Difference between blood and urine toxicology tests

Other toxicology testing methods

Alternative toxicology screening methods are used for specific diagnostic purposes, providing a more comprehensive picture of drugs or toxins in the body.

• Saliva testing is a non-invasive alternative to blood toxicology screening. Saliva is collected using a swab, providing quick results for recent drug and alcohol use. It is commonly used during roadside driving under the influence (DUI) checks and random workplace testing.
• Hair follicle testing: Drug metabolites can be deposited in hair shafts for prolonged periods. Thus, hair follicle testing can reveal drug or substance use that occurred over the past months. ² It helps determine chronic or repeated substance use.
• Sweat testing: This test is performed by analysing the content of a sweat patch that a person wears on their skin for 7-14 days. This method helps determine ongoing substance use during a specific period. It is often applied during recovery programs or probation to ensure abstinence. Additionally, finger sweat testing is a more rapid and less invasive alternative to conventional sweat testing. It has been successfully implemented in monitoring adherence to antipsychotic medication in patients with psychotic disorders. ³

Accuracy and limitations of toxicology screens

How accurate are toxicology screens?

While toxicology screening is generally reliable, its results are subject to variations. The factors affecting accuracy include :

• Type of Test Used: Although immunoassays are ideal for rapid initial screening, they may produce false positives or negatives. Therefore, more accurate confirmatory tests like GC-MS and LC-MS/MS are necessary for validation.
• Detection thresholds: The detection threshold must be carefully selected to determine the minimum concentration to trigger a positive result. Too high a threshold may lead to false negatives, where drug levels below the threshold, yet significantly high, are overlooked.
• Individual metabolism rates are one of the key factors for interpersonal variability. Age, weight, genetics and liver function may affect how quickly a person metabolizes and excretes substances.
• Sample collection and preparation must be thoroughly monitored, as contamination and exposure to temperature and light may skew the results.

False positives and false negatives

A false positive may occur when a toxicology test detects a substance that is not present. Improper sample handling or testing errors often cause it. Furthermore, some prescription or over-the-counter drugs may be mistakenly detected as toxins or drugs of abuse. Cold or flu medications contain ingredients like pseudoephedrine, dextromethorphan or codeine, which may show up in drug testing.⁴ For example, pseudoephedrine used as a decongestant is structurally similar to amphetamines and can falsely yield a positive result.⁵ Therefore, people using these medications must inform healthcare professionals before testing.

Conversely, a false negative occurs when a substance in the sample goes undetected. This can happen due to testing outside the detection window (either too early or too late), sample contamination, metabolic variations or diluted samples.

Mass spectrometry-based tests can confirm initial results or address false results. Upon obtaining a positive screening result, clinicians can run GC-MS or LC-MS/MS as confirmatory methods, as these techniques quantify the substance and identify its chemical structure more accurately.

Conclusion

Toxicology screening plays a critical role in a wide range of settings to monitor and ensure public health and safety. Healthcare professionals may identify harmful substances in the body, which helps them guide treatment steps for individuals, combat illegal substance use and implement workplace safety. Meanwhile, toxicology screening for forensic investigations helps bring clarity to complicated legal cases involving injury and death. Blood and urine toxicology tests are the two most common toxicology screening types, with the former providing a recent snapshot of the contents in the bloodstream and the latter offering a long-term assessment of substance use.

With mass spectrometry and AI-driven data analysis advancements, toxicology screening methods can achieve higher resolution, greater sensitivity and accelerated reporting.

References

1. Galhenage J, Rodrigo A. Prolonged detection of cannabis in urine of a consumer in a forensic hospital, Victoria, Australia, up to 102 days of abstinence-A case report. Psychiatry Res Case Rep 2023;2(1):100089.
2. Hubbard JA. Review on Toxicology Testing in Hair. J Appl Lab Med 2025:jfaf026.
3. Longman K, Frampas C, Lewis H, Costa C, Nilforooshan R, Chambers M, et al. Noninvasive drug adherence monitoring of antipsychotic patients via finger sweat testing. Front Chem 2023;11:1245089.
4. Stoeva S. Common Causes of False Positive and False Negative Results in Amphetamine Screening Tests. Curr Anal Chem 2023;19(8):571-576.
5. Głowacka K, Wiela-Hojeńska A. Pseudoephedrine—benefits and risks. Int J Mol Sci 2021;22(10):5146.

recent-articles