Tox Tuesday: How drugs accumulate and are detected in reservoir matrices

July 19, 2016

Today, drug testing is a common occurrence in schools, hospitals, and various places of employment. Oftentimes these tests are conducted to make sure an individual is not using illegal drugs or alcohol or to prove there are no drugs in their system after an instance of previous drug or alcohol abuse.

There are various ways drug testing can be completed including tests that are made specifically for different reservoir matrices. Some common reservoir matrices include urine, blood, hair, oral fluid, and even sweat. While tests for each reservoir matrix are run differently, the tests are all designed to detect different metabolites or biomarkers that are produced once a certain drug is digested and processed by the body. By discovering these metabolites and biomarkers in the different reservoir matrices, scientists can prove what drugs, if any, have been consumed.

Blood testing was one of the first types of drug tests developed and can accurately detect any drug metabolites in the sample taken. As explained in one article, once a drug is consumed, it is absorbed into cells and tissues similar to the way water soaks across a sponge. They spread from areas of high concentration to low concentration, passing through millions of cell membranes along the way.

As drugs are absorbed they are carried to various sites of action through the bloodstream. This process happens quickly as the heart pumps and recycles the total blood supply in about one minute, thus pumping drug molecules to all parts of the body in various concentrations. Based on this process, blood tests are considered to be one of the most accurate drug tests available, and can detect drugs that were recently consumed. However, because the body moves blood so quickly, drugs are more difficult to detect in a blood sample after a few days.

In addition, these tests are not as widely used today as they involve more specialized equipment and medically trained administrators. According to the American Society of Addiction Medicine, advancements in drug testing technology in the 1970s changed the default testing matrix from blood to urine. Because urine is copious, easily and noninvasively collected, and does not require elaborate sample preparation before testing, it remains the most common means for drug testing today.

Urine testing is also typically the least expensive to analyze, and offers a wide range of drugs for inclusion on test panels. In urine testing, drugs and alcohol can be detected 1-3 days after consumption, depending upon the pharmacological characteristics of the drug, which is one of the shortest windows when comparing urine testing to the testing of other reservoir matrices. The article states that detection periods are variable and also depend on sensitivity and cutoffs of the assay, physicochemical characteristics of the drug or metabolite, pattern of drug use, age, personal metabolism, body mass, and overall health of the individual.

During recent years, oral fluid drug testing has become more widespread as well. This shift has been made possible by improvements in both immunoassay and mass spectrometer technologies, which are now capable of achieving the sensitivities necessary to detect many drugs in oral fluid. Another article explains that oral fluid, sometimes called “mixed saliva,” comes from three major and several minor salivary glands in a person’s mouth and contains many of the same enzymes found in blood, although far less complex.

The salivary glands that produce oral fluid have a high blood flow, so drugs migrate rapidly from the blood to the salivary glands within minutes. The window of detection for drugs in oral fluid is generally 12 to 48 hours, somewhat shorter than for urine. In some cases, this allows for very quick results and allows for on-site drug tests with certain technologies. For example, tetrahydrocannabinol, or THC, the principal psychoactive constituent (or cannabinoid) of cannabis, can be detected in oral fluid just 2-24 hours after use. Oral fluid samples are also much easier to collect when compared to blood and urine tests.

Fingernails are another one of the common reservoir matrixes and have a much longer window of detection. This is because biomarkers become locked in keratin fibers, which make up fingernails, and can be detected up to three to six months after drug or alcohol abuse. This happens because as the nail grows, substances can pass from the blood vessels below the nail into the keratin fibers where they become trapped, another article explains.

Keratin fibers also make up hair and are used in hair testing — another matrices that has a long window of detection. However, in hair testing, there may be no record of drug use in the 5-7 day period before sample collection because it takes that long for the hair to emerge from the follicle in the skin where the hair is produced. Because head hair grows at a rate of about 0.5 inches per month, the standard 1.5 inch hair sample has information about drug use over the prior 90 days.

The article explains that hair testing is most useful in settings where testing is scheduled, because of the longer detection window and explains that it can be easy for some people with substance abuse issues to abstain from drug use for a few days when facing a scheduled oral fluid or urine drug test. It is far more difficult for most drug users to refrain from drug use for 90 days in order to pass a hair test. However, one disadvantage to hair testing is that some drug classes, including benzodiazepines, are poorly detected in hair.

More recently, sweat patches have been developed and are now considered an alternative matrix for drug testing. Sweat has a longer drug detection window than urine or blood for most illicit drugs, and patches are relatively tamper resistant.

The sweat patch is applied to the skin for several days to allow sufficient absorption of excreted drugs. In one study, cocaine was detected in sweat collected from cocaine users after six drug-free days. In contrast, cocaine is usually undetectable in blood/plasma 6-8 hours after drug administration, and the metabolite, benzoylecgonine, is generally not detected longer than 53 hours by commercially available urine tests.

Based on this information, the article states that researchers speculate cocaine and possibly other drugs may be stored in compartments in the skin and slowly released into the sweat gland. However, there is currently a limited number of drugs that sweat patches can test for, and far less test kits developed compare to other reservoir matrices.

Overall, each of these reservoir matrices and the tests that have been developed for them have their distinct advantages and disadvantages. Neogen Corporation is a leader in forensic toxicology and offers forensic drug detection kits for several of these reservoir matrices. For more information, click here.

Category: Toxicology