To ascertain whether an individual has administered drugs of abuse or not, drug testing is commonly employed to check for the presence of any drug(s) of abuse or their metabolites in the donor’s biological specimen such as blood, urine, oral fluid, sweat or hair. There are several types of drug testing.
Urine has been and remains the most widely used body fluid specimen for routine testing for abuse drugs, but oral fluid, sweat, and hair are gaining scientific credibility as alternative specimens following the advancement of testing technology. Let us review the uses and limitations of different specimens for testing below:
Purposes of drug testing
Over the past several decades, drug testing has been used worldwide in various disciplines, including criminal justice, emergency medicine, clinical toxicology, and workplace.
Drug testing plays an important role in facilitating the judicial sentence of drug abusers in courts, drug surveillance programs of inmates who are detained under the custody of drug treatment centers, and the enforcement of the legislation of driving under the influence by police.
Emergency medicine and clinical toxicology
Timely and reliable drug test results are of prime importance in emergency medicine and clinical toxicology. The testing objective is focused on determining the class of drugs that has been inadvertently or purposely ingested or exposed to the patients. Mortalities and morbidities would then be greatly reduced by effective, appropriate, and prompt antidotal treatment or supportive care.
Pre-employment and workplace drug testing has increased rapidly over the last decade in western countries such as the United States of America and the United Kingdom. Federal organizations, government agencies, military, and private corporations exercise drug testing either under mandatory legislation or corporate commitment as a measure to improve safety within the workplace.
Types of specimens for testing
Blood is widely used for drug testing in clinical and emergency toxicology because it offers the best correlation between drug level and pharmacological impairments to the body. The time window for drug detection in the blood is shorter, mostly within several hours than in urine. For example, at a given dosage of cocaine, blood testing can detect use within 12 hours, while urine testing can detect use within 48 to 72 hours. Even though blood is a good specimen for determining the presence of drugs, the concerns about invasiveness of the collection, ease of transportation and storage, and specimen stability greatly hamper its popularity in other fields of application even though substitution and dilution of the specimen to tamper with drug testing are considered impossible.
By far, urine is the most widely used specimen for abuse testing drugs because of the advantages of large specimen volume and relatively high drug concentrations that render drug detection comparatively easier than in other specimens. Also, the technology used in urine testing is well developed and has withstood legal challenges. Furthermore, urine collection is considered non-invasive, and specimens can be collected by non-medical personnel. Urine is a matrix that remains stable over time and can be frozen to maintain the sample’s integrity. Drugs in urine are normally detectable for up to 1-3 days. However, unless the urine sample is obtained under direct observation, adulteration, substitution, or dilution to circumvent, drug testing is possible.
Following the advancement of technology in detecting trace quantity of drug(s) in hair, hair testing has gained attention because of its ability to provide a longer detection window from months to years compared to other specimens. In contrast to providing short-term drug abuse profile through blood and urine testing, hair testing provides complementary information about the long-term drug abuse history. Furthermore, sampling head hair specimen is considered non-invasive, and the drugs incorporated in the hair remain stable and bound for a long time leading to no concern about specimen adulteration. Head hair sampled from the scalp is preferred to obtain the retrospective chronological drug abuse history. Head hair tends to grow at a rate of about 1 cm per month, so a 3 cm section of hair would represent a 3-month history. However, testing for a drug in hair is comparatively time-consuming and costly, and it must be performed in the laboratory because of the unavailability of on-site screening kits.
Oral fluid is increasingly used for drug testing because many drugs in oral fluid correlate well with blood concentrations. Advancement of instrumental sensitivity makes oral fluid a suitable alternative to blood. Oral fluid is a non-invasive specimen that can be sampled under direct observation to prevent adulteration or substitution. The main disadvantage of oral fluid testing is its short detection window, with most drugs being detectable within several hours only. This characteristic renders it suitable for determining very recent drug abuse but weakens its ability to detect use over time. For example, a day ago, someone administered heroin is likely to be tested negative by the oral fluid test but positive by a urine test.
See our article about Types of saliva drug tests.
Collection of sweat is undertaken by attaching a tamper-evident patch, with an underlying absorbent pad inside, to the skin over a relatively long period of time (10-14 days). Analysis of sweat must be performed in a laboratory, and on-site test kits are not available. Sweat testing has not widely been used because of the challenges of the potential contamination from the environment and residual levels of the drug in the skin from prior use.
Characteristics of different specimens for drug testing
The advantages, disadvantages, and time window of detection of different specimens are summarized below.
Screening test versus confirmatory test
To undertake drug testing, there must be a cutoff level for each type of drug to be tested, and such a cutoff point serves as an administrative breakpoint in distinguishing a positive or negative result. Any sample that contains the drug/drug metabolite of interest at the concentration levels equal to or greater than the designated cutoff level is reported as positive, whilst a negative is reported for the concentration level less than the cutoff. Generally, a drug test can be categorized as either a screening test or a confirmatory test, concerning the detection method and testing principle being employed.
Screening test refers to the initial test undertaken to test for a broad class of drugs and their metabolites in the specimen with the presumptive results, i.e., positive or negative. Generally, a screening test is rapid, sensitive, inexpensive with acceptable precision and reliability; however, it lacks precise specificity and may be subject to a false-positive result due to cross-reactivity with other non-targeted drugs of similar chemical structure.
On-site screening test
Use of on-site immunoassay screening kits is highly popular in the fields of workplace testing and emergency toxicology because results are available within several minutes, with reliability similar to laboratory screening, at the site of specimen collection. Furthermore, these kits involve no calibration or maintenance, and no special skills are needed to perform the screening test. Most kits have built-in quality control zones in each panel, which ensures reagent integrity and testing validity. Nowadays, commercially-available on-site screening test kits are usually designed for urine and saliva specimens only, but not for sweat or hair as yet.
Laboratory screening test
Instead of on-site testing, drug screening may also be performed by instrumental immunoassay method in the laboratory by automated, sophisticated, and high throughput analyzers. Generally, laboratory drug screening has to take at least 1-2 days before the results are ready for collection because of the time taken to deliver the specimens to the laboratory, run the tests, and prepare test reports.
Any specimen, which has been presumptively screened positive, should be subject to confirmatory testing to eliminate false-positive results that arise from cross-reactivity. Confirmatory testing should employ highly specific and alternate chemical techniques to obtain unequivocal and accurate analytical results.
Kits for on-site testing
Over the past 10 years, testing kits of different designs have been marketed to meet the growing demand for drug screening at the point of collection. These on-site test kits are commonly used by healthcare professionals and drug treatment and rehabilitation program supervisors to help deter drug use by the patients and supervisees. Dip cards and cassette kits that employ lateral flow immunoassay technology have proven reliable and easy to use. Recently, newly designed testing cups, employing the same technology, with integrated test strips in the interior surface, have grown in popularity because of their ease of testing and sanitary protection to the test operator, eliminating specimen transfer direct contact with the specimen.
See our article about Types of Drug tests.