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Immunoassay Drug Test: What It Is and the Principles

04 April, 2024

A gloved hand holding a test strip near a urine sample

An immunoassay drug test is one of the most common methods to detect the presence of drugs in the system. This test utilises antibodies to specifically detect and measure the concentration of a particular drug or metabolite in biological samples. The principle behind this test is based on the interaction between antigens (drug compounds) and antibodies. The result can indicate a negative or non-negative, which may require further confirmation testing.

Drug abuse screening is an essential part of safety programs in many settings. It aims to identify persons at risk of addiction, ensure workplace safety, and comply with legal requirements. In addition, early detection of illicit drugs can help individuals or employers make informed decisions. As a result, it helps prevent accidents or keep substance abuse issues from escalating. This article will give an overview of immunoassay testing, the principles behind it, and the factors of false-positive results.

What is an Immunoassay Drug Test?

An immunoassay drug test is a type of screening tool that detects various substances in a specimen. It works by utilising antibodies that bind to certain drugs or their metabolites. It can produce rapid results within minutes of analysis. Most often, the results will be indicated through a visible reaction, such as the presence or absence of lines or colour change.

The test utilises portable equipment, such as collection cups, dipsticks, and screening devices. The individual collects and immerses the sample in the test strip containing the antibodies. Users can then get reliable results by strictly following the instructions of the drug test kit.

There are several types of test methods that use initial immunoassay screening. The first one is a urine drug screen. Urine testing is a cost-effective method that can detect a wide range of drugs. It has a window of detection extending up to 120 hours. The second type is an oral fluid drug screen. It is a non-invasive method that can identify recent drug consumption. It has a shorter detection period of 24-48 hours.

Benefits

  • Immunoassay tests are quick, easy to administer, and inexpensive.
  • The test provides quick results, usually available within 5-10 minutes.
  • The test can detect various substances, including common drugs of abuse like concurrent opioids, amphetamines, marijuana, benzodiazepines, and cocaine metabolites.
  • Easy interpretation of urine drug screen and saliva screen results.
  • It is a valuable clinical drug testing tool in primary care management.
  • Allows for quick and efficient monitoring of individuals undergoing rehabilitation from drug or alcohol abuse or chronic opioid therapy.
  • It is a cost-effective method in workplace drug testing. Employers can regularly test their employees without the high fees of laboratories.

A lab technician dipping a screening tool into a sample container

Principles of Immunoassay Drug Tests

The principle behind immunoassay drug tests lies in the interaction between antigens and antibodies. Antibodies are proteins that are part of the immune system and help fight off microbes and foreign substances, such as drugs. When a person consumes illicit drugs, their body breaks down these substances into active or inactive metabolites. These metabolites are detectable in bodily fluids like saliva, blood, or urine samples.

One of the critical principles of immunoassay screening is the specificity of the antibodies. These antibodies target a particular drug that will only bind to that specific substance and no others. The binding will result in a visible change if the drug or metabolite is present. Furthermore, they can be highly sensitive. It means that they can detect low levels of drugs in a sample.

Adulterant detection devices have specified cutoff values for each drug class. It is vital to know these cutoff levels before testing to ensure accurate results. This is especially crucial in professional settings where the test outcomes can influence decision-making. Lastly, immunoassays are ideal for initial screening. If the result indicates drugs, laboratory confirmatory testing is often necessary.

Types of Immunoassays

One common type of immunoassay is the Enzyme-Linke Immunosorbent Assay (ELISA) test. It uses enzymes that attach to antibodies to detect drugs or metabolites in the sample. Another type is the Lateral Flow Immunoassay (LFIA), which is based on the movement of a liquid sample through a polymeric strip. The sample flows along the strip to produce results.

Additionally, the Radioimmunoassay (RIA) is a sensitive technique that measures the concentration of an antigen in a sample. It uses radioisotopes as tracers to monitor the distribution of free and bound antigens. Lastly, the Chemiluminescent Immunoassay (CIA) works by light-emitting reactions.

A bottle spilling different tablets and medicines

False Positives in Immunoassay Drug Tests

There are instances where false positives in an immunoassay drug test may occur. A false-positive result means that the test indicates the presence of drugs when it is not actually present in the person. There are several factors that can contribute to a false-positive immunoassay result. One common cause is cross-reactivity with other substances, such as prescription drugs, over-the-counter supplements, or Nonsteroidal Anti-Inflammatory Drugs (NSAIDs).

Another factor is the sensitivity of the test itself. Some tests may be designed to detect even trace amounts of drugs, leading to false-positive results. Conversely, if the cutoff values are too high, it can lead to false negatives. Moreover, improper testing procedures or handling of samples may contaminate the test and lead to inaccurate results.

The presence of adulterants is also a significant contributor to false-positive results. For example, eating poppy seed products may lead to a positive test for opiates. Likewise, non-smoker exposure to marijuana smoke may result in a positive test for THC. Finally, dilution, addition of extraneous substances, or substitution of samples can lead to false-positive results in commercial immunoassay testing.

Immunoassay vs. Mass Spectrometry

Immunoassay technology is widely used for initial screening due to its speed, simplicity, and cost-effectiveness. It can provide quick results and is suitable for testing a large number of samples. However, it may have limitations when it comes to specificity and sensitivity. It can be easily susceptible to adulterants in saliva and urine drug screening.

To reduce interferences in drug testing, confirmatory tests are often recommended for initial positive screening. It often uses tandem mass spectrometry with gas chromatography or liquid chromatography. It is the process of separating ions based on their mass-to-charge ratio. This technique provides highly accurate and detailed information about a drug.

Conclusion

Immunoassay drug tests are valuable tools for detecting illicit substances in the system. It works by using antibodies to detect abused drugs or their metabolites in the body. In addition, the main methods of immunoassay tests are through saliva and urine testing. Using blood samples is also valuable in confirmatory tests. Moreover, the testing procedure is often preferred in workplaces or primary care because of its speed, convenience, and cost-effectiveness.

While immunoassays are reliable, it is essential to be aware of factors that can lead to false-positive drug screening results. Cross-reacting drugs such as prescribed opioids, the sensitivity of the test, and the presence of adulterants are important factors to consider. When testing for drugs, ensuring the environment is clean and hygienic is essential for accurate results. Lastly, mass spectrometry and chromatography confirmatory testing provides high precision, minimising false-positive or false-negative results.

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