What employers should know about instant drug tests
PoCTs (point-of-care or point-of-collection tests) are sometimes referred to as instant drug tests. They are small, easy to use, portable kits that are used to screen individuals for drugs of abuse at the place of sample collection. Before deciding to use PoCTs, one must understand their limitations as well as their benefits.
The process begins with the collection of an oral bodily fluid sample from the person to be screened. Typically, this is urine or saliva, or sometimes sweat. The collected fluid is absorbed by the kit and the “magic” of the device takes over and a so-called ‘immunoassay screening test’ happens.
Imagine the fluid sample as a bunch of keys and the PoCT as a series of locked doors. Each door represents a specific drug and individual keys represent the chemical make-up of the fluid sample. Each key attempts to open each door and if none of the doors open (because none of the keys fit any of the locks), the sample is deemed to be drug- free (negative)… However, if a key opens a door then a drug has been detected (non negative). Because each door is specific for a different drug, you know which precise drug is being detected.
When a drug is detected, the PoCT will typically display a coloured band to indicate the presence of a specific drug type. Saliva-based PoCT devices have become more prevalent and are commonplace screens because they are easy to use. Just a simple swab is required, which can be done with a witness present to avoid risk of tampering. However, comparative studies show that urine PoCTs are more accurate. Oral fluid has a very rapid response to the use of drugs, however, drugs disappear from oral fluid much more quickly than from urine resulting in a smaller detection window. Despite these facts it may be appropriate to use saliva PoCTs as screens when urinary samples are not made available.
All PoCTs have a ‘cut-off’. This is the smallest concentration at which a drug can be detected by a PoCT device in any given sample. If the concentration of a drug is below the cut-off for that drug, the device indicates a negative result. If the drug concentration is equal to or above the cut-off, then the device indicates a non negative result.
Not all PoCTs are of the same quality and there are no governing international standards for them. Any device used should at least be branded and carry a CE mark. Consider requesting proof of good performance and certification from the supplier.
In conclusion, PoCT devices provide an “instant” result, allowing an employer to react swiftly to possible drug abuse within a company, with minimal workforce disruption. They also cost less than laboratory-based alternatives. However, do consider the costs of any subsequent laboratory confirmatory tests as well as the implications of false positive and false negative results – the latter being a significant drawback.
The inherent inaccuracies of PoCT devices limit their use to a screening role. A screen must be followed by further laboratory-based testing before any final outcome can be confirmed.
With thanks to Dr Dan Hegarty of Express Medicals and Dr Simon Davis of Imperial College, London.