Tox Tuesday: The advantages of ELISA drug testing

The enzyme-linked immunosorbent assay (ELISA; pronounced like the name “Eliza”) is a testing technique used to detect and measure substances in biological samples. It’s been one of the most trusted testing methods for nearly half a century and is popular in many fields, for everything from food allergen detection to medical screening for various illnesses. It’s a very sensitive and versatile test.

In the decades since the method was developed, it’s become known for valuable applications that fill some needs that newer technologies simply don’t. ELISAs can accurately detect a wide variety of target analytes in many sample types. For the toxicology market specifically, ELISA is an excellent and cost-effective solution to meet high throughput screening needs.

How ELISA works

There are a few different kinds of ELISAs. One used in forensic toxicology testing is the direct competitive ELISA. This procedure is simple and is easily automated or can be run by a lab technician. It operates based on competition between an enzyme conjugate (such as horseradish peroxidase, or HRP) and the targeted substance in the sample. These two substances compete for a limited number of specific binding sites on a precoated microplate. Other types of ELISA include indirect and sandwich.

Why ELISA?

Because of its simple method and potential for automation, ELISA is a cost-effective screening method specifically for high throughput testing applications. Alternative methods may appear to be cheaper (or faster) options on a per-sample basis, but when screening is scaled up to the volumes needed in real-world applications — at practical sensitivity and detection requirements — ELISA can offer far greater efficiency both in terms of cost and speed. The equipment required is relatively inexpensive, flexible, and can easily be made to accommodate much larger volumes if operations choose to invest in automated set-ups. The argument that alternative methods are cheaper or faster might be true in some laser-focused situations, without considering high sample volumes, the capital cost of equipment, the high cost, and the expertise needed to analyze the data and manage complicated equipment.

ELISAs can specifically target a wide range of analytes using many different types of samples. This includes a long list of drugs of abuse, like THC, methadone, opioids, benzodiazepines, designer drugs, and synthetic cathinones. The tests offer excellent performance on the many sample matrices that come from humans: hair, blood, urine, oral fluid, serum, plasma, and other forensic samples. Some laboratories have also seen success with less common matrices, like breast milk, fingernails, and many others that pose challenges for alternative testing methods.

The selectivity of ELISAs is hard to beat, especially with complex samples. In one of his papers, Dr. Timothy Cross points out that using unknown or new samples with analytical methods presents a problem, as there is no direct way of identifying the specific antigen from a sea of others without investing in even more technology.

ELISAs have a relatively low investment to get started with, as they don’t require the expensive instrumentation required by more advanced analytical methods. Training to use ELISAs is also very straightforward, requiring the ability to pipette consistently and perform simple sample dilutions.

While newer technologies have been developed during the long lifetime of ELISAs, none so far have managed to hit all the requirements for efficient and sensitive results needed, especially by those with high volumes of samples to test. But even outside of a high throughput situation, ELISAs remain a reliable and simple solution for the forensic, food safety, medical, and life science fields.

With over 100 assays available detectability of over 300 major drug analytes and metabolites, Neogen offers ELISA drug testing kits for all major drugs of abuse.