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Field Sobriety Tests/Chemical Testing Breath or Blood


If you are stopped and suspected of driving under the influence (DUI) in Ventura County, the arresting officer will likely ask you to submit to two types of tests: field sobriety tests and a chemical test of your breath or blood. Both types of tests are intended to judge whether you are in violation of California’s DUI laws.

Field Sobriety Tests/Chemical Testing Breath or Blood

Even if you “fail” one or more of these tests and get arrested for DUI in Ventura, our Ventura DUI attorney may still be able to help you avoid a conviction for DUI. Strongest Defense can challenge both types of tests in a variety of ways, and present a variety of other potential defenses to your Ventura DUI.


There are three standardized FSTs that are approved for use in a Ventura DUI: Horizontal Gaze Nystagmus (HGN), the One Leg Stand, and the Walk and Turn. As “standardized” tests, police officers are supposed to administer FSTs with the same method every time, and also look for the same designated cues during their performance. As an experienced Ventura DUI attorney who is P.O.S.T. certified in Field Sobriety Tests, David Lehr understands how FSTs are supposed to be administered, and he knows how to use your performance on FSTs to your advantage in Ventura DUI proceedings.

Horizontal Gaze Nystagmus (HGN)

  • Among the three FSTs, the HGN test is probably the most accurate in showing the presence of alcohol.
  • The HGN test involves the officer holding his pen, finger, or flashlight about a foot from your face and moving it from side to side while checking your eyes as you attempt to follow it. The test should be performed while you are standing at eye level with the arresting officer.
  • The officer must tell you to keep your head still and track the object as it moves from side to side by moving your eyes only. What the officer is looking for is called nystagmus, which is the involuntary jerking or bouncing of the eyes as they attempt to track a horizontal movement.
  • The three standardized impairment cues for HGN are lack of smooth pursuit, onset of nystagmus prior to forty-five degrees, and nystagmus at maximum deviation; any four cues (counting each eye separately) may indicate impairment.
  • HGN can be present at very low alcohol levels, so the fact that an officer might observe HGN does not necessarily show that someone is impaired due to ingestion of alcohol.
One Leg Stand
  • The officer should explain that you are to stand with both hands at your sides, and then raise one foot six to eight inches off of the ground for thirty seconds.
  • The officer should also demonstrate how the test is performed after explaining it, and should ask you if you understand how to do the One Leg Stand before asking you to perform it.
  • The four standardized cues for the One Leg Stand are hopping, putting your foot down, raising your arms, and swaying; any two or more cues may indicate impairment.
  • There are numerous additional factors that can affect your performance on the One Leg Stand FST.
Walk and Turn
  • The officer should explain that you are to start standing with both hands at your sides and with the heel of your right foot touching the toe of your left foot. The officer should also demonstrate how to stand in the starting position after explaining it, and the officer should note whether you can maintain your balance in the starting position.
  • In addition to explaining the Walk and Turn, the officer must also demonstrate how to perform the test, including the turn.
  • During performance of the test, the officer should explain that you are to take nine heel-to-toe steps out along an imaginary line, keeping your hands at your side the entire time. On the ninth step, you should make a pivot turn, and then take nine heel-to-toe steps back along the same imaginary line.
  • The eight standardized cues for the Walk and Turn include starting too soon, missing heel to toe, stepping off of the line, raising your arms from your sides, taking the wrong number of steps, making an improper turn, and stopping walking; any two or more cues may indicate impairment.
  • There are numerous additional factors that can affect your performance on the Walk and Turn FST.

Non-Standardized FSTs

Many Ventura police officers continue to use outdated and unreliable FSTs during DUI arrests. These non-standardized FSTs include the Finger-to-Nose test, the Rhomberg test (tilt your head back and count to 30), and the Hand-Pat test. We are routinely successful in having these excluded as DUI evidence.

Chemical Testing – Breath or Blood?

Once you are arrested for DUI in Ventura County, you have the choice between taking either a breath test or a blood test to determine your BAC.

Evidential Breath Test

The breath test that is given after arrest in a Ventura County DUI is called an evidential breath test. There are substantial manufacturer guidelines specifying how evidential breath test devices are supposed to be used, and there is a huge body of law that controls how the machines are to be operated, maintained, and calibrated. One of the things we do in every Ventura DUI case involving a breath test is to subpoena the maintenance and calibration logs for the device that was in use during the time period that you were arrested. Our experienced Ventura DUI lawyer examines the logs to determine if your test was performed in compliance with California law. If it was not, we can have the test results excluded from your Ventura DUI case.

Blood Test

If you choose the blood test, the arresting officer will take you to one of the local hospitals where a nurse will draw your blood. The officer is supposed to retrieve the vial of blood with your identifying information on it, and book it into evidence. Initially, the test will typically be performed for alcohol only. However, if the results indicate a BAC level of less than 0.08%, it is possible that your blood will be tested for drugs other than alcohol. Whenever the facts of a particular Ventura case call for it, we have our clients’ blood tested by an independent laboratory, and we are often successful in challenging the results of blood tests following Ventura DUI arrests.


While most people believe that a blood test is the better option, there are advantages and disadvantages with both blood and breath tests in Ventura DUI cases:

  • Advantages of the Breath Test in Ventura DUIs:
    • If your alcohol level is rising, the breath test will be performed sooner than the blood test. If the breath test is performed before your BAC level rises to 0.08%, you might not be charged with a DUI in Ventura.
    • It is possible to attack both the accuracy of the testing device and the competency of the officer using it.
  • Advantages of the Blood Test in Ventura DUIs:
    • If your alcohol level is falling, the blood test will be performed later than the breath test because you need to be transported to a hospital in order for it to be administered. If your BAC level drops below 0.08% before the test is administered, you might not be charged with a DUI in Ventura
    • Your sample can be retested by an independent laboratory, both for alcohol level and to determine if the blood was properly drawn.

In many cases, if not entirely exculpatory, the results of your chemical test can be used to help reduce your charges if you are facing a possible felony conviction. Read more about misdemeanor vs. felony DUI.

Free Consultation with a Ventura DUI Lawyer

For more information about how we may be able to challenge the FSTs or chemical test results in your case, please contact us today to schedule a free consultation.

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