Roadside drug testing has become an increasingly important part of drug-driving enforcement in the UK. Where a police officer suspects that a driver may have drugs in their system, a roadside screening device such as the DrugWipe may be used to test an oral fluid sample.
A positive roadside DrugWipe result can lead to arrest and the taking of a subsequent blood sample for forensic analysis. However, the roadside test itself is a screening test, and its reliability depends upon the device being used and interpreted correctly.
Small departures from the required procedure may therefore become relevant when reviewing the circumstances surrounding a drug-driving allegation.
How does a roadside DrugWipe test work?
DrugWipe is a lateral-flow screening device designed to detect the presence of specified drugs in oral fluid. The sampling element is passed over the tongue to collect oral fluid before the test is activated and allowed to develop.
As with other lateral-flow devices, there are prescribed procedures governing how the device should be handled, developed and interpreted.
So, what could potentially go wrong at the roadside?
1. Touching the DrugWipe sampling pads
The sampling pads are the part of the device used to collect the oral fluid specimen.
If a police officer touches the DrugWipe sampling pads before or during the test, this may represent a departure from the manufacturer’s handling instructions.
Direct contact with the sampling area introduces a potential contamination issue. It may also raise questions as to whether the device was handled strictly in accordance with the prescribed procedure.
Where the circumstances of a roadside drug test are being reviewed, it may therefore be important to establish exactly how the device was handled before the sample was collected.
2. Reading the DrugWipe result too early
Timing is another important aspect of the DrugWipe procedure.
The test needs sufficient time to develop before the result is interpreted. If the DrugWipe is read before the specified 8-minute development period has elapsed, the test may not have fully developed.
Consequently, the significance and reliability of a line observed prematurely may be open to question.
This is why contemporaneous evidence concerning when the test was activated and when the result was actually read can be important when assessing whether the roadside procedure was correctly followed.
3. Reading the DrugWipe result too late
Reading the device substantially later than the prescribed time can also create difficulties.
Lateral-flow tests are designed to be interpreted within a specified time frame. Changes occurring after that period should not automatically be regarded as representing a valid test result.
If there is uncertainty over when a DrugWipe result was interpreted, it may therefore be appropriate to consider the timings recorded by the police and any available body-worn video footage.
4. Failing to keep the DrugWipe horizontal
The position of the device while the test is developing can also be relevant.
The manufacturer’s procedure requires the DrugWipe to be placed on a level surface during development. If the device is instead held in the hand, tilted, carried around or otherwise moved, this may constitute a departure from the prescribed procedure.
This is potentially important because lateral-flow devices depend upon the controlled migration of liquid through the test strip.
The question is therefore not simply whether a line eventually appeared, but whether the device was used under the conditions required for the result to be properly interpreted.
Does an incorrectly performed DrugWipe test invalidate a drug-driving case?
Not necessarily.
A roadside DrugWipe is principally a screening test. In a drug-driving investigation, the subsequent evidential blood sample and its laboratory analysis will generally be of central importance.
However, apparent departures from the roadside testing procedure can still warrant examination, particularly where there are questions concerning the circumstances leading to arrest, the reliability of the roadside result or the consistency of the prosecution evidence.
Relevant material may include police statements, contemporaneous records, body-worn video footage, the timings of the test and information identifying the device and procedure used.
Expert review of drug-driving evidence
Drug-driving cases can involve much more than simply comparing a reported blood concentration with a statutory limit. Depending upon the circumstances, an expert review may consider the roadside testing procedure, continuity and storage of specimens, toxicological analysis, analytical uncertainty, prescribed medication, patterns of drug use and the interpretation of reported drug concentrations.
Where there are concerns about the way in which a roadside DrugWipe test was conducted, the surrounding evidence can be reviewed alongside the subsequent forensic toxicology results to determine whether any issues are of potential significance.
At Bericon Forensics, our independent forensic experts provide specialist review and expert evidence in drug-driving cases for solicitors throughout the UK.
