Ever wondered if breath and blood test results in a DUI case are truly as solid as they sound? Many people assume that once a number shows up on a machine, the case is over. But DUI testing is not perfect, and mistakes can happen at several stages. From the traffic stop to the lab analysis, each step must follow strict legal and scientific rules.
A DUI charge can carry serious consequences, including license suspension, fines, higher insurance costs, and even jail time. That is why challenging breath and blood test evidence can be a critical part of the defense. Josh Lee & Associates’ DUI attorneys carefully examine not just the final number on a test result, but the entire process behind how that number was produced. When procedures are not followed correctly, the reliability of the test can come into serious question.
Challenging the Legality of the Traffic Stop
Before any breath or blood test is even given, the officer must have a lawful reason to stop the driver. Police cannot randomly pull someone over without reasonable suspicion of a traffic violation or criminal activity. If the stop itself was unlawful, everything that follows may be challenged in court. This includes field sobriety tests, breath tests, and even blood draws.
Attorneys carefully review dashcam footage, bodycam recordings, and police reports to see whether the officer had a valid reason for the stop. If the officer claimed weaving or speeding, the defense may look for proof of that behavior. When the stop lacks proper justification, a judge may suppress the test results. That can significantly weaken the prosecution’s case from the start.
Questioning Field Sobriety Test Procedures
Field sobriety tests often happen before a breath or blood test, and they can influence whether an arrest is made. These tests include the walk-and-turn, one-leg stand, and horizontal gaze nystagmus test. However, they must be administered according to standardized guidelines. Small errors in instructions or demonstrations can affect performance.
Attorneys analyze whether the officer properly explained the test and whether outside factors influenced the results. Poor lighting, uneven pavement, medical conditions, fatigue, or anxiety can all impact how someone performs. If the field tests were flawed, the probable cause for arrest may be challenged. Without valid probable cause, the breath or blood test may also come under scrutiny.
Attacking Breathalyzer Calibration and Maintenance
Breath testing machines are not infallible, and they require regular calibration and maintenance. If the device is not properly maintained, it may produce inaccurate readings. Defense attorneys often request maintenance logs, calibration records, and service history for the specific machine used. Any irregularities can raise serious questions about the reliability of the result.
Before we go further, here are common issues attorneys look for with breath test devices:
- Missed or delayed calibration checks
- Improper maintenance or repairs
- Software malfunctions or outdated firmware
- Failure to observe the required waiting period before testing
- Environmental factors that could affect readings
Even small deviations from protocol can matter in court. If the officer did not observe the driver for the required time before the test, substances in the mouth could affect the reading. Medical conditions like acid reflux can also cause falsely elevated results. These technical details often become central in DUI defense.
Challenging the Officer’s Training and Certification
Not every officer is equally trained in administering breath or blood tests. Officers must be properly certified and follow strict guidelines during testing. If the officer’s certification expired or training was incomplete, the defense may argue that the test was improperly conducted. That can impact how much weight the court gives to the results.
Attorneys may request training records and cross-examine the officer about their experience. Inconsistencies between the report and testimony can weaken the credibility of the evidence. Proper procedure includes timing, documentation, and accurate recordkeeping. When an officer cuts corners or forgets steps, it can create reasonable doubt.
Examining Blood Draw Procedures and Chain of Custody
Blood tests are often viewed as more reliable than breath tests, but they are not immune to challenges. The blood must be drawn by a qualified person, stored properly, and transported under controlled conditions. If the sample is mishandled or contaminated, the results can be compromised. Defense attorneys closely examine every step from the moment the blood is drawn to when it is tested.
Chain of custody is especially important in blood test cases. This refers to the documented handling of the sample from collection to analysis. Any gaps or inconsistencies in the chain can raise questions about whether the sample was mixed up or altered. If the prosecution cannot show a clear and secure chain of custody, the results may be challenged in court.
Disputing the Accuracy of Lab Testing
Once a blood sample reaches the lab, it must be analyzed according to strict scientific standards. Lab technicians must follow detailed procedures, and equipment must be properly calibrated. Human error, contamination, or faulty equipment can lead to inaccurate results. Attorneys often review lab reports and may consult independent experts to examine the findings.
In some cases, defense teams request independent testing of a retained portion of the blood sample. This can reveal discrepancies or confirm whether the original result is questionable. Even small differences in measurement can matter when a case depends on being just over the legal limit. Scientific evidence may appear precise, but it is still subject to error and interpretation.
Arguing Rising Blood Alcohol Levels
Alcohol does not instantly reach its peak concentration in the bloodstream. In some situations, a driver’s blood alcohol concentration may have been below the legal limit while driving, but rose later by the time testing occurred. This is known as the “rising blood alcohol” defense. It can be especially relevant when there is a delay between driving and testing.
Attorneys analyze the timeline carefully, including when the person last drank and how much time passed before the test. Food intake, body weight, and metabolism can all affect alcohol absorption rates. Expert witnesses may be used to explain how alcohol levels change over time. This argument can create doubt about whether the driver was actually over the limit at the time of driving.
Building a Comprehensive Defense Strategy
Breath and blood test challenges are rarely based on just one issue. Strong defense strategies often combine multiple arguments, including improper stop, flawed procedures, equipment problems, and scientific uncertainties. Each detail matters, and small weaknesses can add up to a larger defense. The goal is not just to question the number on the test, but to question the entire process behind it.
Identifying procedural errors, scientific flaws, and constitutional violations allows a defense team to work effectively in protecting a client’s rights at every stage. DUI cases may seem straightforward on the surface, but careful legal analysis can reveal opportunities to challenge the evidence and pursue a stronger outcome. Taking action early provides the defense with more room to investigate and build a case. When breath and blood tests are examined closely, they often do not tell the full story.