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Why does the urine sample give an inconclusive DUI?

Given the choice it would be a wiser man who elects for the urine test in place of other chemical forms of testing. If you happen to be weighed down by the realization that you have had too many drinks passing through the gullet, it is better to opt for the urine test, and there is a solid reason why that decision could turn the tables when you are charged with DUI.

Many experts in DUI handling seem to agree, across the board, that of the three major tests- blood specimen testing, urine sample analysis and the breathalyzer reading – the urine analysis happens to be the least accurate and by that token the least preferred evidence tabled in a court. For this reason most jurisdictions have seen the urine analysis losing pride of place to other forms of chemical testing that are judged to be more reliable and superior and unlikely to elicit confusing readings.

Urine testing gradually became the test of the last resort when other samples are not available or were not possible. Even the use of urine samples to test for drugs receded because of fears over the inadequacy of the results, particularly when it became imperative to know whether the driver was under the influence of a drug at the material time of testing. The scientific explanation underlying the declining importance of the urine test is that concentration of alcohol or drugs in the urine could not be reliably correlated with the concentrations in blood as tested under laboratory conditions.

Difficulties correlating the alcohol count in urine and blood:

Experience has shown that the blood and urine concentration of alcohol in DUI charge need not necessarily be correlated and the count can vary remarkably. The basic finding is that the concentration of alcohol in urine is normally three times (1.33 times to be absolutely factual) the Blood Alcohol Concentration (BAC). So, to convert urine reading into a BAC reading you need to multiply the urine count by 1.33. The problem with this approach and calculation is that you get saddled with a figure that represents an average count.

The defense counsel can argue in court that the prosecution shouldn’t be presenting an average reading but a reading that is specific to the defendant and material to the moment when he was Terry stopped for DUI. The same urine sample (another untested portion of it) will most likely be preserved so that defendant can later conduct his independent test. The opportunity should be leveraged as it could throw up an alternative conclusion that could buttress defense arguments.

In some laboratory experiments it was proved that people showed 40% to more than 55% higher alcohol in their urine sample as their blood sample alcohol readings. All this creates a situation of ambiguity that opens up urine sample results to being challenged in a court of law.

A helpful review of our bladder function

To the lay observer the sample taken from the emptied bladder represents the sample connected to the material moment when the accused was terry stopped and arrested for DUI, but a closer review of scientific facts would say otherwise.

The urine that is extracted from the bladder cannot be assumed to be the urine produced at the moment of arrest. There is a simple reason why this is so. The bladder urine content at any moment of time will be a composite of urine produced throughout the day from the time you previously emptied the bladder. So what the police are testing is essentially a changing hue of readings pertaining to urine that was excreted at different times. That way the urine sample is a less accurate reading of alcohol content than a blood sample reading, and ambiguous readings are open to be contested by defendants in all cases.


The unreliability of urine alcohol testing is illustrated through the following examples:

1. Driver consumed alcohol many hours before taking the wheel

For argument’s sake let’s assume that the driver imbibed a heavy dose of alcohol of around four pegs of boilermaker (potent cocktail of beer and whiskey) four hours before taking the wheel. The blood alcohol concentration would be lower because ample time is available for breaking down the alcohol in the liver. But the driver has not urinated ever since his four hour long alcohol shot and his bladder, bursting at the seams, will show a higher alcohol reading disproportionate to BAC.

2. Driver consumed alcohol an hour before taking the wheel

If the driver drank recently or has downed a peg or two minutes before a Terry stop, the alcohol may not have been processed fast enough to have reached urine to the bladder and a urine sample will give a lower reading than what the BAC would reveal.

If alcohol intake is followed by a larger intake of water or soda, the diluting impact would lower urine readings further. Sometimes to allay suspicions the police take a follow up sample some twenty minutes after the first sample. So, delaying the urine sample testing could work against the driver that drank recently. In these circumstances the blood test and breath analyzer would be more accurate and reliable than the urine test (but for the accused, less defendable in court!).

The burden of proving DUI charges lies with the prosecution – they need to prove that there was alcohol abuse, over and above the fact that abuse was instrumental in impairing the judgement of the driver. Apart from unsteady gait, slurred speech, inability to walk in a straight line back to the car and other physically visible symptoms of alcohol abuse that will be recorded by the police, the clinching evidence will be the presence of alcohol in higher concentrations in the breath, blood and urine, exceeding the permissible norm. If given a choice, the urine test will be the favored option for the driver because of the ambiguity in urine readings and their scientific interpretation and the opportunity that is presented to legally rebut the allegations.

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