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DUI blood tests are not foolproof

When a driver in Illinois has an encounter with law enforcement while the driver is in actual physical control of a motor vehicle as required by Illinois DUI (Driving Under the influence) law (625 ILCS 5/11-501), the officer may be looking for signs of DUI impairment. This can begin with the initial driving behavior. Common markers of alcohol-related driving behavior include driving too slowly, wide turns and weaving.

This will provide the reasonable suspicion the officer needs to stop the driver. Terry v. Ohio 392 US 1, 20 L.Ed. 2d 889 (1968) The police will also observe the manner in which the driver executes the stop. This includes matters such as how quickly the driver notices the flashing lights and slows, how the driver performs while engaged in pulling over (using turn signal for instance) and how effectively the driver stops and parks the vehicle.

Next, the officer will have an opportunity to observe the driver face-to-face. Signs of impairment would be slurred, thick tongued speech, bloodshot and glassy eyes, heavy eyelids and an odor of alcohol. An officer will also note any difficulty the driver encounters in retrieving the driver’s license, insurance card and registration.


The officer will be cognizant of the driver’s knowledge of where he or she has been, is currently located and is headed. They may inquire about date and time of day and will certainly ask about alcohol consumption. Most will not ask, have you been drinking but rather, how much have you had to drink, a leading question designed to elicit an incriminating response.

After these and related questions, the driver will be directed to stop out of the vehicle (refusing to do so can constitute the crime of obstruction of justice and or disobeying a police officer). Thereafter the driver will be required to perform the HGN, the walk-and-turn and the one-legged stand. These are collectively known as the standardized field sobriety tests.

The final test prior to the DUI arrest will be the Preliminary Breath Test, or PBT. This is not the “official” test to determine blood alcohol content (BAC) because the PBT results are not considered sufficiently reliable for that purpose.

On the other hand, if the test is administered in accordance with Illinois State Police regulations, by a machine that has been properly calibrated and tested, the results are admissible to prove the driver’s BAC. Any BAC of at least .08% is a violation of the DUI law should the driver fail to get the results suppressed before trial or if admitted at trial, to impeach their credibility.

Another means that the police have for proving the BAC is a blood test. It is up to the discretion of the officer whether to use breath or blood tests. The Supreme Court held, in Missouri v. McNeely, that the police could not obtain a blood draw without a search warrant. Due to the time and expense involved, unless there is an accident, police agencies do not ordinarily rely upon blood draws.

However, they may do so and almost always will if the suspect driver is taken to the emergency room for treatment. These blood draws are subject to attack; they are not the be all to end all.

The blood must be drawn properly. The police must establish a chain of custody to demonstrate who handled and transported the blood vials. Questions can arise about the temperature at which it is transported and stored. Finally the testing itself must meet scientific standards.

Related posts:

Can I get my Illinois DUI dropped if they violate my rights? August 3, 2012, Illinois DUI Lawyer Blawg
Summary of requirements for admission of DUI breath tests in Illinois, April 12, 2013, Illinois DUI Lawyer Blawg

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