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Your results may not be accurate…

27 April 2016

Most lawyers do not understand science. After all, why would they? – It’s not something that’s taught in law school! Over the years I have dealt with hundreds of forensic reports in relation to drink and drug driving cases. Reports usually contain lots of medical and scientific jargon and can be extremely difficult to understand. Any case involving blood or urine will include forensic reports – this makes up a large part of the prosecution’s case against you. If your solicitor fails to understand the science, how can he properly defend you?

A specialist doctor or scientist who is qualified to give evidence in court can be extremely helpful when defending a drink and drug driving cases. For example, I will often use an expert witness when a back calculation (of alcohol or drugs) is required to prove that my client was under the limit at the time of driving. I will also use expert evidence to assess the accuracy of breath, blood or urine specimens.

I’d like to give you an example of a case that I dealt with that no one thought I could win.

Case: Understanding the science proves the CPS wrong

My client was asked to provide a blood sample following a serious collision. The police had served all the relevant documents relating to their case (MGDDA, MGDDB, witness statements, lab reports, etc). Most lawyers would, in this situation, advise a guilty plea. Anyone who knows M.A.J Law also knows that this is not our style. Challenging cases is at the heart of what we do. It was only by studying the science behind the results was I able to identify a possible error with my client’s case. Let me talk you through this case.

The police use a series of instruction manuals (known as MGDDA & B documents) when taking a specimen of breath, blood or urine from a suspect in police custody. The MGDDA document in my client’s case (below) recorded a roadside reading of 64ug. You can see that the test was completed at 2139 hours.

Screen Shot 2015-04-08 at 16.22.16-1

The MGDDA document also recorded my client’s breath readings at the police station. The lowest alcohol reading at the time of the test was 43ug. The test was completed at 2314 hours.

Screen Shot 2015-04-08 at 16.27.29

After filling out the MGDDA document (above), the officer then moved onto the MGDDB document (this contains the urine procedure). The first urine specimen was obtained at 2328 hours.

Screen Shot 2015-04-11 at 20.59.08

The second urine specimen was obtained at 0028 hours. This was later sent to the lab for analysis.

Screen Shot 2015-04-08 at 16.34.59

The lab report, which I obtained at the first court hearing, stated that my client’s sample contained not less than 154 milligrammes of alcohol per 100 millilitres of urine (154 mg%). The legal limit in urine is 107 milligrammes .

Screen Shot 2015-04-08 at 16.41.25

My client was charged with drink driving and bailed to court.

I represented my client at the first court hearing. As soon as I read the MGDDA and MGDDB documentation I had a suspicion that the results were not correct. Let me explain.

You will note from the above MGDDA document that my client provided readings of 64ug at 2139 hours and 43ug at 2314 hours. Therefore, 21ug of alcohol appears to have been eliminated from his breath during the 95 minute interval. From this figure I was then able to calculate that my client had a breath-alcohol elimination rate of 13.3ug% per hour.

By understanding the correlation between breath and blood, I was able to determine that my client’s blood-alcohol elimination rate 31mg% per hour. Based on scientific studies and accepted data, an elimination rate of 31mg% per hour is at the extreme end of the general population. Blood alcohol elimination rates typically range from 10-20mg% per hour with the most likely rate being 14mg% per hour.

Indeed, elimination rates can vary within the general population and it is quite possible that my client eliminated alcohol very quickly. A study in 1990 (Neuteboom and Jones: Forensic Science International) considered blood results from over 1,000 drivers. A blood alcohol elimination rate of 30mg% per hour or more was observed in only 0.7% of cases.

So, what’s more likely? Either my client happens to eliminate alcohol quicker than almost every other person, or, the CPS got the results wrong.


Breath test devices

Currently all roadside devices used by the police are not type-approved. Results from a non-type approved device are not evidential – meaning they cannot form the basis of a criminal prosecution. It is for this reason that you cannot be charged based on your roadside reading.

Roadside devices do not conduct self-calibration checks and cannot detect interfering substances or mouth alcohol (which can falsely increase the reading).

Although manufacturers recommend that these devices are checked on a monthly basis, most police forces wait 6 months before recalibration. It is always possible, even likely in fact, that the roadside device used in your case had not been maintained in accordance with police guidance.

In my client’s case, there was no evidence to suggest that the device had malfunctioned or over-estimated his breath reading. In addition, his last alcoholic drink was some 60 minutes before the roadside test (which makes ‘mouth-alcohol’ unlikely). I was happy, therefore, to accept that the roadside test was an accurate basis upon which I could conduct further calculations. This was very helpful when I also considered the urine result.

Tip: Whilst the roadside reading is ‘non-evidential’ it can be used as a basis to conduct further comparative calculations.

Production of urine

This is where it gets interesting.

It’s a simple fact that urine is produced in the kidneys and is then passed to the bladder where it is stored until urination occurs. The significance of this fact is often missed when considering a drink drive case based on urine results. Let me briefly explain why.

The alcohol in your urine may not equate with the alcohol contained in your blood. For example’s sake, let’s assume you drank a large whiskey-coke at 11pm. By 1am – two hours later – the alcohol is not detectable in your blood as your body has completely eliminated it. The difference with urine is that it does not reduce overtime – it’s stored in your bladder and effectively ‘sealed off’. So, unless you’ve been to the toilet, by 1am you would have the same level of alcohol in your urine as you did when you first drank the whiskey-coke. The only way of removing the alcohol is to urinate. It is for this reason that your bladder should always be emptied fully prior to the evidential urine specimen. Only then, can it truly reflect the level of alcohol in your system at the time of the test. For the results to be accurate, the second urine specimen should be taken from freshly produced urine (produced whilst at the police station), and not from urine stored in your bladder from an earlier time. The first urine specimen should be discarded.

I have handled many cases where the police officer has asked my client to fill a specimen pot with the first specimen and, immediately after, provide the second specimen. Remember – the law allows 1 hour before you produce the second sample. I have even had cases where my client was told to start to urinate in the toilet, then stop, then start again and fill the specimen pot!

The science behind the procedure is not brand new.  In 1967, the British Medical Association produced a report entitled ‘The Drinking Driver’ The report recognised that urine alcohol concentration trailed well behind blood alcohol concentration. The report recommended that two specimens be taken at least 30 minutes apart.

This, of course, still does not happen!

Any specimen of urine analysed by a laboratory (for use in a prosecution) should include a 6% deduction. In my client’s case, you will note that the lab report stated his result was 154 milligrammes of alcohol per 100 millilitres of urine (154 mg%). Therefore, his actual urine specimen would, according to the analysis before deduction, have shown a reading of at least 163 mg%.

If you have been charged with drink driving following a urine test, carefully consider whether you fully emptied your bladder before giving the second specimen. In my client’s case, his breath reading at the station was 43ug. The equivalent in urine is 131mg. We know that his level is dropping based upon his roadside result being higher. Allowing for alcohol elimination during the hour prior to the second urine specimen, I would expect his reading to have been under the legal limit (at around 95mg). It was actually 154ug!! The equivalent in breath is 50ug.

So, how is this possible?

I instructed an expert witness to review the evidence and produce a report. My suspicions were proven to be correct. The expert concluded that the urine sample could not have been accurate based upon the previous breath readings. He said that there were three plausible explanations for this;

  1. The sample tested by the laboratory did not belong to my client
  2. The lab had failed to use an approved method of testing (and failed to deduct 6mg)
  3. The level of preservative added to the sample by the police was not sufficient. The sample ferments before it arrives at the laboratory. A byproduct of fermentation is alcohol production.
  4. My client’s bladder was not fully emptied prior to the second sample. This means that the second sample was contaminated with old, stored urine, containing a higher alcohol concentration.

I served the report on the CPS and this was the outcome. Case dismissed.







In my client’s case, I had raised the issue of an incorrect specimen from the start. I had stated on the case management documentation at the first court hearing that my client did not empty his bladder at the first specimen. However, you will appreciate that there is a big difference between simply asserting that he did not empty his bladder and actually having scientific evidence to prove it.

By understanding the science behind the calculations of alcohol in breath, blood and urine, and how alcohol diminishes over time, it is possible to successfully challenge the prosecution’s case. Remember, it is for the prosecution to prove a case beyond reasonable doubt. If we can establish doubt, even a relatively small doubt, then the court should not convict.

In my client’s case he was found not guilty.


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