DUI Chemical Testing in Illinois

In Illinois, chemical testing plays a central role in the prosecution of driving under the influence (DUI) cases. These tests are used to determine the presence and concentration of alcohol, cannabis, prescription medications, and/or illegal drugs in a driver’s system. The outcome of a chemical test can impact not only whether charges are filed, but also the length of a summary suspension, and the severity of penalties on a DUI criminal charge.

This page addresses the legal framework surrounding DUI chemical testing in Illinois, including the types of tests that law enforcement may request, the distinction between roadside and official tests, legal thresholds for various substances, penalties for refusing testing, and how the results may be used in court. The role of a DUI defense attorney is also explained in the context of analyzing chemical test results for potential errors and preparing a legal defense.

Forms of Chemical Testing in an Illinois DUI

Under Illinois law, police officers investigating a suspected DUI may request the driver to submit to one or more chemical tests. The three primary forms of chemical testing include:

• Breath testing: Typically used to estimate blood alcohol concentration (BAC) through a breath sample, most often administered using a breathalyzer machine at the police station.
• Blood testing: Used to measure the presence and concentration of alcohol, cannabis (THC), prescription medications, and controlled substances.
• Urine testing: Less commonly used but still permissible, especially in cases involving suspected drug use or when blood testing is not feasible.

These tests must be administered in accordance with Illinois Department of State Police regulations, and the testing equipment must be properly maintained and calibrated to ensure accuracy.

Portable Breath Tests Versus Stationhouse Breath Tests

There is a critical legal distinction between the portable breath test (PBT) conducted at the roadside and the evidentiary breath test administered at a police station.

• The portable breath test is used during a traffic stop to establish probable cause for arrest. The results of a PBT are not admissible at trial to prove BAC but may be used to support the officer’s decision to make an arrest. This device is considered less accurate and is not approved for evidentiary purposes under Illinois law.
• The evidentiary breath test, conducted at the station using a certified breathalyzer machine, is admissible in court to establish the defendant’s BAC. The machine must comply with administrative regulations under Title 20, Part 1286 of the Illinois Administrative Code.

The distinction between these tests can influence the legal strategy, especially in challenging whether probable cause existed for the arrest and whether the admissible test was properly administered in an Illinois DUI case.

Legal Limits for Alcohol, Cannabis, and Drugs in Illinois

Illinois law sets specific legal thresholds for various substances that may impair a driver. The presence of these substances at or above the legal limits may trigger a per se violation of DUI law under 625 ILCS 5/11-501.

• Alcohol: The average Illinois driver is considered over the legal limit if the BAC is 0.08 percent or greater. Commercial driver’s license (CDL) holders are subject to a lower threshold of 0.04 percent while operating a commercial vehicle, and drivers under the age of 21 are subject to a zero tolerance standard (no alcohol may be present while driving a motor vehicle while under the age of 21).
• Cannabis (THC): The legal limit is five nanograms or more of THC per milliliter of whole blood, or ten nanograms or more per milliliter of another bodily substance. These thresholds apply regardless of whether cannabis use was recreational or medical.
• Illegal drugs: The presence of any amount of a controlled substance such as cocaine, heroin, or methamphetamine may lead to a DUI charge, regardless of impairment.
• Prescription drugs: If a prescribed medication impairs the driver’s ability to operate a vehicle safely, a DUI charge may result, even if the medication was lawfully prescribed.

Summary Suspension for Refusing Chemical Testing

Illinois enforces an implied consent law under 625 ILCS 5/11 501.1, which states that anyone who drives on Illinois roads is deemed to have consented to chemical testing when arrested for DUI. A refusal to submit to chemical testing triggers an automatic statutory summary suspension of driving privileges.

• First offense: A 12 month suspension for refusing to submit to chemical testing.
• Second or subsequent offense within five years: A 3 year suspension.

These suspensions are administrative and apply even if the DUI charge is later dismissed. An individual facing a summary suspension may request a hearing to contest the suspension within ninety days of the notice of suspension.

What Constitutes a Refusal to Test

A refusal to submit to chemical testing does not require an explicit verbal or written statement. The following actions may also be deemed a refusal:

• Failure to complete the test as instructed
• Uncooperative behavior or deliberate interference with the testing process
• Delays or attempts to negotiate the testing
• Agreeing to one form of testing but refusing others that are requested

Illinois law allows law enforcement to request multiple forms of testing, and refusal to submit to any of the requested tests may be considered noncompliance under the implied consent statute.

DUI Charges Below the Legal Limit

A DUI charge may be brought even when the test result is below the legal limit. This is known as an impairment-based DUI. Under 625 ILCS 5/11 501(a)(2), it is unlawful to operate a vehicle while under the influence of alcohol or drugs to a degree that renders the person incapable of driving safely.

Evidence supporting an impairment-based DUI may include:

• Field sobriety test performance
• Erratic driving behavior
• Observations by the arresting officer
• Statements made by the driver
• The presence of drugs or alcohol in the vehicle

This provision allows prosecution even when chemical tests are below the statutory per se limits, or when the chemical test has been refused.

Challenging the Reliability of Chemical Tests

Chemical test results can be challenged in court based on a variety of grounds. These challenges may be based on procedural violations, equipment malfunctions, or operator error. Common defenses include:

• Failure to comply with the standard for breathalyzer testing in 20 Ill. Adm. Code 1286
• Failure to observe the driver for 20 minutes before administering a breath test
• Use of expired or uncalibrated testing equipment
• Contamination of blood or urine samples
• Lack of proper certification for the test administrator
• Chain of custody errors for blood or urine samples

Such challenges can lead to the exclusion of test results, reducing the strength of the prosecution’s case or leading to dismissal of charges.

Effect of Chemical Test Results on Sentencing

In Illinois, chemical test results can affect sentencing outcomes, especially if the test reveals a particularly high BAC. Under 625 ILCS 5/11-501(a)(1) and 730 ILCS 5/5-5-3.2, the presence of an aggravating factor such as a BAC of 0.16 or higher can result in enhanced penalties. A few examples appear below:

• A first-time DUI offender with a BAC of 0.16 or higher may face a mandatory minimum fine of 500 dollars and mandatory minimum community service of 100 hours.
• Enhanced penalties also apply if there was a passenger under 16 years old in the vehicle at the time of the offense.
• If the BAC is 0.16 or greater and the person is convicted of DUI, the offense qualifies as an aggravated factor that can increase the severity of the sentence under 730 ILCS 5/5-5-3.2(a)(1).

Importance of Legal Representation in DUI Chemical Testing Cases

An experienced DUI defense attorney plays a critical role in evaluating the circumstances of chemical testing and identifying potential legal challenges and/or defenses. Legal representation is essential for several reasons:

• Analyzing whether the testing was lawfully requested and administered
• Reviewing maintenance and calibration records for testing equipment
• Cross-examining the officer or technician who administered the test
• Identifying procedural violations that may justify the exclusion of test results

The admissibility and reliability of chemical test results are central to most DUI prosecutions. Legal counsel with experience in DUI defense and knowledge of Illinois administrative code provisions governing chemical testing can provide a strategic advantage in court.

Consult with an Illinois DUI Defense Attorney

Chemical testing is one of the most important evidentiary components in a DUI case in Illinois. Legal defenses often center on the reliability and admissibility of chemical testing results, and enhanced penalties may apply for high BAC levels or the presence of aggravating factors. Even when test results are below the legal limit, a DUI charge may still be filed based on observed impairment. The assistance of a DUI defense attorney is critical in reviewing testing procedures and advocating for the best possible outcome.

Wirth Law provides experienced legal guidance for individuals facing DUI charges. Our office serves clients in Chicago, Naperville, and throughout Illinois who are navigating the aftermath of a DUI. We regularly assist individuals in Cook, Will, Kane, Kendall, Lake, Kankakee, Dekalb, and Winnebago Counties, offering dedicated representation to those facing complex driver’s license suspension or DUI revocation issues. Wirth Law also represents out-of-state residents who have an Illinois hold on their driving privileges, helping clients across the country navigate the process of clearing their Illinois record so they can drive legally again.

Our practice is known for its exceptional client service and strong record of success in DUI defense and license reinstatement matters. Jennifer Wirth, managing attorney, has received multiple awards recognizing her commitment to client advocacy, including perfect “10” ratings on Avvo and Justia, the Martindale-Hubbell Client Champion Award, and selection as one of the top DUI defense attorneys in Chicago by Expertise.com. Her approach to legal representation is grounded in professionalism, compassion, and an in-depth understanding of Illinois Secretary of State hearing procedures.

At Wirth Law, every client is treated with respect and care. Our firm prioritizes clear communication, ensuring that individuals fully understand their legal options so they can make informed decisions about their case. Whether dealing with a first-time suspension or a more complex revocation after multiple DUIs, clients can expect honest guidance and skilled representation throughout the DUI reinstatement process.

Wirth Law offers free consultations, affordable flat fees, and payment plan options through Affirm to make legal services more accessible. To schedule a consultation, contact Wirth Law at (312) 761-8290 or email jennifer@wirthlaw.org.

Further Reading: Illinois DUI Defense

• Area of Practice: Illinois DUI Defense
• Overview of a First DUI in Illinois
• Illinois Statutory Summary Suspension Law
• Aggravated DUI in Illinois
• Out-of-State DUI: Suspensions and Revocations
• Type A Injury DUI Cases
• CDL Consequences for an Illinois DUI
• Underage DUI and Zero Tolerance
• Marijuana DUI
• Prescription Drug DUI
• DUI Chemical Testing