Breath vs. Blood: Which Test Is Easier to Challenge in Colorado?

Chemical test results often play a central role in Colorado DUI prosecutions, but not all tests are equally vulnerable to challenge. After a DUI arrest, drivers are typically required to submit to either a breath test or a blood test, and each method comes with its own strengths, weaknesses, and potential sources of error. Breath tests rely on properly calibrated equipment and correct administration procedures, while blood tests depend on accurate collection, handling, storage, and laboratory analysis. Problems at any stage can raise questions about the reliability of the results. 

Understanding the differences between breath and blood testing, and the legal challenges commonly associated with each, can help drivers better understand how chemical evidence may affect the outcome of a Colorado DUI case.

The Two Types of Chemical Tests Colorado DUI Stops Use

When a Colorado police officer thinks a driver may be drunk or on drugs, there are two main ways to test for that: breath tests and blood tests.

A breath test is given on the side of the road or at a police station. The officer uses a machine called the Intoxilyzer 9000. The driver blows into the machine, and it measures how much alcohol is in their breath. This gives a reading of the driver’s blood alcohol concentration, or BAC.

A blood test works differently. A trained professional draws a small sample of the driver’s blood. That sample goes to a lab where scientists check it for alcohol or drugs. Blood tests are more precise than breath tests and can detect a wider range of substances.

Both tests follow specific steps that must be done correctly. If those steps are skipped or done wrong, the test results may not hold up in court.

The Intoxilyzer 9000 must be properly maintained and calibrated. Blood samples must be stored and handled in a specific way to stay valid.

Knowing how each test works, and where mistakes can happen, matters a great deal for anyone dealing with DUI charges in Colorado.

What Colorado’s Express Consent Law Actually Requires

Colorado’s express consent law controls what happens when a driver is arrested for DUI or DWAI. The law is found in C.R.S. § 42-4-1301.1. It applies to anyone driving a vehicle in Colorado.

What the Law Says

When a police officer lawfully arrests someone for DUI (Driving Under the Influence) or DWAI (Driving While Ability Impaired), that driver has already agreed, by choosing to drive, to take a chemical test. This agreement is called “implied consent.” The driver does not sign anything. The act of driving creates the agreement.

Three Things the Law Requires

1. The driver must take a full chemical test chosen by the officer. This test measures alcohol or drug levels in the body through breath or blood.
2. If the driver refuses, their license is revoked. This happens separately from any criminal charges. A refusal can result in license suspension even if the driver is never convicted of DUI.
3. Before testing begins, the officer must tell the driver what happens if they refuse.

Why This Matters

Each choice a driver makes at this moment has real legal consequences. Knowing what the law requires, and what it does not allow, is the starting point for any legal challenge to a chemical test result.

The law sets firm rules for both drivers and officers. When either side steps outside those rules, the test result may be open to challenge in court.

Can You Refuse a Chemical Test in Colorado?

Yes, a driver can refuse a chemical test in Colorado. But refusing comes with serious penalties, even if the driver is never convicted of a crime.

Colorado’s Express Consent Law requires all drivers to submit to chemical testing when a law enforcement officer has probable cause to suspect drunk or drugged driving. Refusing to take the test does not mean avoiding consequences. The law automatically punishes refusal through the Colorado Division of Motor Vehicles (DMV), separate from any criminal court proceedings.

What refusal means in court: A prosecutor can tell the jury that the driver refused the test. The jury may take that as a sign the driver knew they would fail, which makes the criminal case harder to defend.

What refusal does NOT prevent: A Colorado judge can issue a search warrant allowing police to draw blood by force. This is called a compelled blood draw. It is used most often in serious cases involving injury, death, or repeat DUI offenders. When this happens, the refusal no longer blocks the evidence.

Refusing a chemical test rarely benefits the driver. The penalties for refusal are often harsher than the penalties for simply taking the test.

Why Breathalyzer Science Isn’t as Reliable as You Think

Most drivers think a breathalyzer reading is hard science, a number that proves whether someone was drunk. The truth is that breathalyzers have real weaknesses that defense lawyers use to challenge DUI cases.

1. The Body Ratio Problem

Breathalyzers calculate blood alcohol content (BAC) by assuming every person converts breath alcohol to blood alcohol at the same rate: 2,100 parts blood to 1 part breath.

But human bodies work differently from person to person. For some people, this fixed formula pushes the reading higher than their actual BAC.

2. Mouth Alcohol Contamination

Alcohol sitting in the mouth, from burping, acid reflux (GERD), or dental fixtures, can mix into a breath sample.

The machine reads this leftover alcohol as if it came from the bloodstream, which it did not. This false reading can push results over the legal limit even when true BAC is lower.

3. Calibration and Maintenance Failures

Breathalyzer machines, like the Intoxilyzer 9000 used in Colorado, must be tested and serviced on a regular schedule.

When police departments skip or poorly document this maintenance, the machine’s accuracy becomes questionable. Courts can throw out results tied to poorly maintained devices.

A breathalyzer number is a calculated estimate, not a perfect measurement.

Colorado courts recognize these limitations, which means a BAC reading from a breathalyzer can be legally challenged.

How Colorado Police Are Required to Administer Breath Tests

Colorado police must follow strict rules when giving a breath test. Breaking these rules can make the test results invalid in court.

The Observation Period

Before the test, the officer must watch the person for 20 straight minutes. During this time, the person cannot eat, drink, smoke, or vomit.

These actions can leave alcohol in the mouth. Mouth alcohol causes falsely high readings on the breath test machine.

The Testing Machine

Colorado uses a machine called the Intoxilyzer 9000. This machine must be properly certified and calibrated.

That means it has to be checked and set up correctly before it can be used. Police departments must keep written records proving the machine was working properly at the time of the test.

Officer Training

The officer running the test must hold a valid certification to operate the Intoxilyzer 9000.

Without that certification, the test results may not hold up in court.

Why This Matters in Court

Defense lawyers often ask for the paperwork tied to these requirements.

They look for problems such as:

• A shortened observation period

• Missing or incorrect calibration records

• An officer who lacked proper certification

When any of these problems exist, a lawyer may be able to get the breath test results thrown out.

These records are public, measurable, and routinely checked, which is why breath tests are often challenged in DUI cases.

Common Ways to Challenge a DUI Breath Test in Colorado

A DUI breath test result can be wrong, and a defense attorney can challenge it in court. Just because an officer gave you a breath test does not mean the result is accurate or legally usable.

1. The Officer Did Not Follow the Rules

Colorado law requires the officer to watch you for 20 minutes before giving the test. This waiting period is called the “deprivation period.” It makes sure you have not eaten, burped, or put anything in your mouth that could change the reading.

If the officer skipped or shortened this step, the result may be thrown out.

2. The Breathalyzer Was Not Properly Maintained

Breathalyzers are machines, and machines need regular testing and upkeep. Colorado requires officers to keep written maintenance and calibration records for every approved device.

If those records are missing or incomplete, the machine’s accuracy is in question. No records means no proof the device was working correctly.

3. A Medical Condition Skewed the Result

Certain health conditions can make a breath test read higher than your actual blood alcohol level. These include:

• GERD (acid reflux) — stomach gases can carry alcohol vapors into the mouth

• Diabetes — can produce acetone, which some breathalyzers mistake for alcohol

• Mouth alcohol — leftover alcohol from dental work, mouthwash, or burping

Each of these challenges attacks a different weak point in the prosecution’s case.

A defense attorney reviews the arrest records, device logs, and your medical history to find which failure applies to your situation.

How Blood Tests Are Collected and Handled After a Colorado DUI Stop

When police suspect drunk driving in Colorado, they may ask for a blood test. This test must follow specific rules from start to finish. These rules exist to make sure the blood sample is handled correctly and can be used as reliable evidence in court.

The Blood Collection Process

A trained medical professional called a phlebotomist draws the blood. They must use a sterile kit that contains no alcohol-based cleaning agents. Using alcohol to clean the skin before a DUI blood draw could interfere with the test results.

Chain of Custody: Tracking the Sample

Every person who handles the blood sample must document what they did with it. This tracking process is called a chain of custody. It creates a paper trail showing exactly where the sample has been and who touched it.

CDPHE stands for the Colorado Department of Public Health and Environment. This agency sets the approved testing standards labs must follow.

If any step in this process is skipped or done wrong, the blood sample may not be considered reliable. A defense attorney can challenge the results if proper procedures were not followed.

Colorado law gives defendants the right to request independent retesting of their blood sample. This means a separate lab, chosen by the defense, can test the same sample. This right makes proper handling of the sample essential for both sides of the case.

Common Ways to Challenge a DUI Blood Test in Colorado

When you are charged with a DUI in Colorado, a blood test result is not automatically accepted as fact. Defense attorneys look for specific problems with how the blood was collected, stored, tested, and handled. Any one of these problems can weaken the prosecution’s case or remove the test result from evidence entirely.

Defense attorneys review collection records, lab protocols, technician credentials, and whether your constitutional rights were followed. A confirmed problem in any one of these areas can lead a judge to suppress the blood test result, which means it cannot be used against you in court.

How Rising BAC Can Work in Your Favor in a Colorado DUI Case

When you drink alcohol, your blood alcohol content (BAC) keeps rising for 30 to 90 minutes after your last drink. Your body needs time to absorb the alcohol into your bloodstream.

This means your BAC at the time of a breath or blood test may be higher than it was when you were actually driving.

Colorado law sets the legal limit at 0.08% BAC. If police waited a long time before testing you, your BAC may have still been climbing during that wait.

Your BAC while driving could have been below the legal limit, even if the test result shows otherwise.

Defense attorneys call this the “rising BAC” argument. It works like this:

• Your BAC was still going up between the time you stopped driving and the time you were tested

• The test result captures a later, higher number — not your actual BAC while behind the wheel

• The longer the gap between the traffic stop and the test, the bigger the difference between those two numbers

This defense is most useful in cases where police took a long time to collect a blood or breath sample after pulling you over.

A skilled DUI defense attorney can use timing records, absorption rate science, and witness statements to challenge whether the test result truly reflects your condition while driving.

Defense Strategies Colorado Attorneys Use to Dispute Test Results

A positive BAC (blood alcohol content) test does not mean an automatic conviction in Colorado. Defense attorneys have several ways to fight both breath and blood test results in court.

Challenging Breath Tests

When police use a breath testing machine called the Intoxilyzer 9000, attorneys look for problems like:

• Poor calibration – Was the machine properly set up and maintained before the test?

• Operator certification – Did the officer have a current, valid license to run the machine?

• Observation period – Colorado law requires officers to watch a driver for a set time before testing. If that step was skipped or rushed, the results may be invalid.

Challenging Blood Tests

Blood test results can also be questioned. Attorneys examine:

• Chain of custody – Was the blood sample properly tracked from collection to the lab?

• Blood kit expiration – Was the collection kit within its usable date?

• Lab accreditation – Was the testing lab officially approved to run these tests?

• Refrigeration – Was the sample stored at the correct temperature to prevent contamination?

Broader Legal Challenges

Both test types can be challenged when:

• Police stopped the driver without legal cause.

• Constitutional rights, such as the right to refuse or speak to an attorney, were violated.

• The testing process was not followed correctly.

Role of Expert Witnesses

Defense attorneys bring in toxicology experts — scientists who study how alcohol behaves in the body — to explain issues like:

• Fermentation contamination — when natural processes in blood cause false alcohol readings.

• Partition ratio variability — the rate at which alcohol moves from blood to breath differs between people, making breath tests less precise.

• Coagulation problems — clotting in blood samples can affect test accuracy.

Each of these challenges gives the jury reason to doubt whether the test results are accurate and reliable.

When doubt exists, charges can be reduced or cases can be dismissed. A strong defense does not need to prove the test was wrong — it only needs to show the test may not be trusted.

What Happens After a Chemical Test Gets Thrown Out in Colorado

Getting a chemical test thrown out is a major turning point in a Colorado DUI case. When a judge suppresses this evidence, prosecutors have to take a hard look at what proof they still have.

What “suppression” means: A judge can block certain evidence from being used in court when it was collected illegally or improperly. In DUI cases, this often applies to blood, breath, or urine test results.

Three Common Outcomes

1. Charges Get Reduced

Without a chemical test showing blood alcohol content (BAC), prosecutors may offer a plea deal for a lesser charge. Common alternatives include:

• DWAI (Driving While Ability Impaired) – carries lighter penalties than a full DUI

• Reckless driving – a traffic offense with no DUI label attached

2. The Case Gets Dismissed

If the suppressed test was the main piece of evidence against a defendant, prosecutors may not have enough left to move forward. Courts require sufficient proof before a case can proceed to trial.

3. Prosecutors Rely on Other Evidence

The state may still pursue the DUI charge using:

• Officer observations during the traffic stop

• Field sobriety test results (walking a straight line, eye tracking, etc.)

• Dashcam or bodycam footage

• Witness statements

How Early You Hire a Colorado DUI Attorney Affects Your Test Defense

When you hire a Colorado DUI lawyer matters, especially when chemical test results are part of your case.

A lawyer hired right after your arrest can act fast to protect important evidence. Blood samples can be saved for independent retesting, but they break down over time if not stored properly.

Breathalyzer maintenance and calibration records can be deleted during routine cleanups, so those records need to be requested quickly. A lawyer hired early can also file a challenge to your DMV license suspension before the seven-day deadline passes. Missing that deadline means losing your right to fight the suspension, and the criminal case and the DMV process run on separate tracks.

Lawyers brought in late often face a case where the key evidence has already been locked in against you. A lawyer hired early can send investigators to check road and weather conditions at the arrest scene, pull dashcam footage from the officer’s patrol car before it gets overwritten, and find witnesses who saw what happened.

Chemical test results, whether from a breathalyzer or a blood draw, are not automatically accurate. Equipment can be faulty. Blood samples can be mishandled. Officers can make procedural mistakes.

Each of these issues can be challenged, but only if your lawyer has time to investigate them. The longer you wait to hire a DUI attorney in Colorado, the fewer options you have to build a strong defense.