Drug Driving Technical Defences

How accurate are police blood tests?

If you want to win your drug driving case, your solicitor must understand the science behind a blood test (unsurprisingly, this is not something that’s taught in law school!). Drug Driving cases are often won on complex technical points relating to the reliability and integrity of scientific results, measurements and checks. M.A.J. Law would estimate that approximately 30 – 40% of our drug driving case victories relate to analytical data and testing methodologies. If your solicitor does not understand this process you are, without a doubt, less likely to win your case.

Take a look at the Streamlined Forensic Report (SFR1) below. You can see the result of the blood test (in this case, THC). If charged by the police, you should receive an SFR1 (if you haven’t received one, call us immediately). This report will contain the result of the analysis.

Why does it look official? Probably because an unofficial-looking document wouldn’t make you feel as guilty!

In reality, the SFR1 proves very little . It could even be used to win your case.

The prosecution's SFR1
The prosecution's SFR1

The Results/Findings section is where you will see the level of THC (or any other drug tested for). In this case, 4.8 micrograms. Other than the result and reference numbers, the SFR1 is a standardised template, enabling the police to present results with the lowest possible effort (and cost). Here’s how we use the SFR1 to win cases.

The National Streamlined Forensic Reporting Guidances gives the police and practitioners a greater understanding of the streamlined forensic disclosure regime (although I’d like to know how many officers have actually read it). It explains that there are two possible alternatives to the SFR1;

  1. You ‘agree’ the report, meaning the results are entered into evidence, or;
  2. You contest the report, outlining why the results cannot be agreed. This automatically renders the SFR1 inadmissible and should force the CPS to produce a more detailed forensic report known as the SFR2.

Can you guess which alternative causes the CPS the biggest problem? Below are the key issues our team often identify with the streamlined forensic reports. To discuss your results in more detail, please call our office to speak to a member of our team.

The SFR1 process explained in Video - Watch Now

M.A.J. Law’s drug driving technical defences

The following technical defences have been developed and refined by our team of specialist solicitors, toxicologists and expert witnesses. They are used to win drug driving cases on a daily basis. They may well surprise you.

But, before we come on to that, it is worth mentioning that many cases are won without a ‘defence’. A common theme throughout our website relates to CPS funding shortages. The vast majority of our drug driving cases fail because the CPS miss deadlines, misunderstand procedures and miscommunicate between agencies, without good reason. We’d be happy to explain this in detail should you want more information.

Now, back to defences…

1. Using certified reference materials to prepare calibration standards for quality control

Certified reference materials are controls or ‘standards’ that are used to validate analytical measurement methods, or for the calibration of instruments. A certified reference material is a particular form of measurement standard.

Unlike with breath samples (where the reading is automatically produced by a device) the analysis of blood samples is comparative; meaning a forensic scientist (or laboratory assistant) must interpret data to form opinions. A drug driving blood analysis is a comparative result.

Comparative results are exposed to a greater degree of uncertainty.

In order to measure the amount of analyte (drug) in a blood sample, the laboratory must first create a calibration standard. To do this, they use ‘calibrants’ to establish reference points. A calibrant is a substance with a known and certified drug concentration (a certified reference material) upon which other results are compared.

There are two reasons why this form of measurement standard does not produce reliable results;

i. The reference material may not be ‘certified’.

UKAS provides accreditation to organisations producing Reference Materials, who wish to demonstrate their competence through formal compliance.

Interestingly, UKAS hands the policing of Reference Materials to laboratories, stating that the laboratory is responsible for ensuring the suitability of the Reference Material Producer.

Reference materials play an important role in underpinning the accuracy and validity of measurements made within testing and calibration laboratories. When selecting and purchasing reference materials and/or calibrated artefacts, to have confidence in the materials/artefacts, laboratories need to ensure that the producer of the material is competent and that the material has been produced using a valid procedure.

In some circumstances, when setting the calibration ‘standard’, the laboratory may use a reference material that is not certified (as a cost cutting measure). The issue with a non-certified reference material is that its uncertainty level is not recorded. All measurements have some degree of uncertainty that may come from a variety of sources, no single analytical technique is 100% accurate. Uncertainty levels can vary widely depending on many factors, but it is important that the laboratory analysing your sample understands the uncertainly level so that this can be factored into the interpretation. Without knowing the uncertainty level of the reference material, we cannot determine the quality of the experiment, the accuracy of the results, or the degree of analytical variation.

ii. The reference material may have deteriorated

A second issue that frequently arises when challenging the reliability of a drug driving blood sample relates to the ‘recycling’ of certified reference materials. As above, the difference between a certified and non-certified reference material is its traceability – the ability of the material provider to authenticate the material’s origin and confirm uncertainty factors. Reference materials can deteriorate (drugs break down) which would in consequence mean that a higher than true concentration would be reported in case samples. Therefore, best practice states that different reference materials should be used to prepare calibration standards and quality controls, but this is not yet a mandatory requirement. A laboratory may choose to continuously recycle a reference material, using is over and over again to prepare calibration standards. Who doesn’t like getting their money’s worth?

M.A.J. Law will often ask a laboratory to establish the reliability of its chosen reference material by by providing a ‘Certificate of Analysis’. These can be used to check expiry dates, validity and origin.

By analogy, think about a vehicle’s service history. It allows a buyer to understand more about the vehicle’s usage, maintenance, reliability etc… Without it, you cannot make an accurate assessment of the vehicle’s value. A ‘Certificate of Analysis’ is a reference material’s service history.

Certificate of Analysis

2. ‘Blanks’ between drug driving blood sample tests

All drug driving blood tests are carried out in large batches (meaning multiple samples are analysed at any one time). A blank solvent should be injected into the instrument before each test is conducted (clearing the equipment of any substance previously analysed).

Despite legitimate concerns raised by independent forensic scientist and toxicologists, most well-known laboratories still fail to use ‘blanks’ between tests. An issue arises where a very high concentration blood sample is tested immediately before a very low concentration or ‘marginal’ blood sample. Without a blank solvent in between, some of the drug previously analysed will ‘carry-over’ to the next test, thereby resulting in a higher than true concentration.

M.A.J. Law knows of some laboratories that have analysed a range of samples (bloods, urines, liver extracts etc.) without blanks in between. In some instances, massively high drug concentrations present in urine samples were carried over to the next case sample, producing an elevated drug concentration or a false positive result.

3. Results based on averages

Your drug driving blood sample will be analysed anywhere from 3 to 8 times. Once these results are generated, a mean average result will be calculated. This method could mean that you are wrongly and unfairly charged with drug driving.

Consider the following;

Your drug driving blood sample is analysed three times to measure the THC value. The legal limit for Cannabis (THC) is 2.0 micrograms. The following results are generated:

First Test: 1.9 micrograms of THC

Second Test: 2.8 micrograms of THC

Third Test: 2.0 micrograms of THC

MEAN AVERAGE: 2.2 micrograms (over the limit). See the unfairness?

This analytical method means that despite only one result actually exceeding the prescribed limit, you are still charged with drug driving. In drink driving breath cases, you are required to provide two specimens of breath on an evidential breath testing device, the lowest of which is used in evidence. So, if you give a breath reading of 39 micrograms and a breath reading of 44 micrograms, you would not be charged (as the lowest is under the prosecution limit of 40 micrograms). In the interests of fairness, they will always choose the lowest result.

In drug driving blood cases, they will not choose the lowest result. In these circumstances, my argument is very clear – can the courts be satisfied beyond reasonable doubt that you were over the legal limit when the majority of tests conducted by the police’s laboratory actually places you under the limit? Do you think the court would convict you in these circumstances?

4. Lack of proficiency testing

One of the biggest concerns highlighted by our team of forensic toxicologists relates to the lack of a specific proficiency testing scheme for drug driving cases.

Proficiency testing measures the performance of individual laboratories for specific tests and is used to monitor laboratories’ continuing performance. In a proficiency test, one or more samples are sent to a number of participating laboratories. Each laboratory measures the sample according to a given set of instructions and reports its results to the administrator.

The results reported by each laboratory are compared to the reference value for that sample. Those laboratories with results that fall within a defined range will pass. Those who results fall outside of that range, will fail.

Drink driving alcohol casework is tested extensively with monthly proficiency testing schemes. In contrast, the only schemes available for drugs in forensic toxicology cases don’t involve drug concentrations relevant to drug driving cases. Meaning, on other words, no one actually monitors the performance and results of drug driving police laboratories.

5. ISO Accreditation

All laboratories have to be specifically accredited in order to carry out drug driving testing. This accreditation is known as ‘ISO 17025’. Until 2017, it is very easy for any laboratory to fall back on this ISO approval rating when facing a challenge to results. However, following the recent Randox Scandal (involving the manipulation of results by a leading laboratory), this accreditation is no longer sufficient. Laboratories in England & Wales are now, more than ever, under the microscope.