Testing for drugs of abuse is performed globally to screen for the presence of drugs in a variety of settings, forensic toxicology, workplace drug testing, anti-doping, and clinical toxicology. Commercial methods of testing for drugs of abuse have undergone significant change over the last decade, to stay abreast of the constant increase in new substances being abused, alternative matrices, and market demands. Public awareness, workplace drug testing, and regulatory requirements have led to an astronomical increase in the number of drug tests routinely performed per annum and, as a result, drug testing has become a multibillion dollar industry.
Whether in a clinical, anti-doping, forensic, or workplace setting, immunoassay remains as the most widely practiced method of screening samples for drugs of abuse (DoA). Drugs-of-abuse testing is a two-tiered process: The laboratory must conduct an initial test (screening test), followed by a confirmatory test on the sample before the specimen can be reported as positive. Immunoassay is a flexible technique that can provide a rapid, inexpensive, and convenient method to screen large numbers of samples in a variety of matrices.1 Based on the principle of antibody-antigen reaction, immunoassay can detect the presence of drugs and drug metabolites in a biological sample, thus preventing the need for further, more complicated, and expensive confirmatory testing.
History and the modern immunoassay
Urine drug testing can be traced back to the 1970s and was famously used in testing soldiers arriving back from service during the Vietnam War. At this time, the technologies used were radio Immunoassay (RIA) and enzyme multiplied immunoassay test (EMIT). Today, RIA has now become almost obsolete; and the most commonly used laboratory based techniques for urine drug testing are enzyme linked sorbent immunoassay (ELISA), EMIT, and cloned enzyme donor immunoassay (CEDIA). All of the above methods are now automated to meet the demands of a modern toxicology laboratory.
Historically, urine has been the most common matrix for drug testing as it is easy to collect and to analyze, and can be collected in large volumes. This is still true for clinical toxicology, rehabilitation, and, to an extent, workplace drug testing. In the last 10 years, new matrices such as oral fluid and hair are increasing in prevalence for workplace drug testing and medico-legal sectors.
In the field of forensic toxicology, blood is required to determine the current state of impairment of an individual for legal cases. It is commonplace in post-mortem toxicology to have an absence of blood and urine; in this situation, the toxicologist must analyze forensic matrices such as postmortem blood, tissues and vitreous humor. The “analysis of post-mortem samples is one of the most challenging tasks in forensic toxicology,”2 and, in turn, immunoassay manufacturers have been further developed new methods for these matrices. The ELISA-based technologies have proved to be the most versatile technology.
There is a new market requirement for high-quality drugs-of-abuse testing to be performed outside the laboratory setting. Traditionally, this is undertaken by lateral flow immunoassay tests (e.g., urine strip tests/drug cups) but the advances in oral fluid testing has led to a number of portable handheld readers currently on the market. The devices can detect a panel of up to 9 of the most popular drugs of abuse, these are being used by police forces worldwide.
Modern automated immunological technologies have advanced drug-screening procedures further by providing accurate results at high speeds. Lab-on-a-chip technologies have been developed to consolidate a number of drug tests onto miniature chips and consolidation of drug-testing platforms in a lab. These multiplex immunoassays based on ELISA principles are capable of detecting multiple drugs of abuse from a single undivided patient sample, leading to more time- and labor-effective screening.
The future of drugs-of-abuse testing
Today, the technology is routinely available for laboratories to cost effectively screen a range of biological samples for drugs of abuse. The emergence of multiplexing methods has set a new standard in immunoassay testing with greater sensitivity and broader detection for drug screening. Lab-on-a-chip methods offer a high throughput multiplex capability that cannot be matched by traditional methods.
As designer drugs and new variations of drugs continue to enter the market, toxicologists are required to broaden their test menu past the “NIDA 5” (a five-panel drug test for marijuana (THC), cocaine, amphetamines, methamphetamines, and opiates (heroin, morphine), all in a single test.) to take this into consideration. As new sample matrices continue to be explored, multimatrix platforms will further advance laboratory testing capabilities. With significant benefits to be gained through consolidated testing, fully automated multiplex methods are likely to prevail, offering highly accurate and rapid drug testing in a range of test settings.
Erin Montgomery studied forensic science and has significant experience in the fields of forensic toxicology and drug testing. She works at Randox Laboratories as a product specialist for biochip array technology.
References
- Cowan D, Osselton D, Robinson S. Drug Testing; Addiction and Drugs Project (2005).
- Stimpfl T, Vvcudilik W. Automatic screening in postmortem toxicology. Forensic Sci Int. 2004;142(2):115-125.
