One of the factors that may lead to a DUI arrest and even a conviction is the results of your breath test. However, these tests are prone to different errors, enough to cast doubt on the results. And if you are not keen, you may be convicted due to results that are falsely high or inaccurate. For this reason, it is wise that if arrested for DUI, you reach out to an experienced DUI defense attorney. The attorney may be able to scrutinize the results and discover where the mistake is, which can later help your case.

At San Jose DUI Attorney Law Firm, we have skilled lawyers who understand the several factors that can render the results of a breath test null and void. They will thoroughly evaluate the results and the circumstances of your arrest and find even that one thing that can help your case. If you are arrested for DUI in San Jose, do not hesitate to contact us.  As you read on, you will understand when breath tests are taken and mistakes that can render the test results invalid.

When to Administer a DUI Breath Test in a Drunk-Driving Case

Police officers use two forms of breath testing in drunk-driving cases. These tests are administered during two distinct stages of a DUI investigation. They include:

  • During a drunk-driving traffic stop or a stop at a sobriety checkpoint. This roadside breath test is known as a preliminary alcohol screening (PAS) test and is taken before one is arrested.
  • At a hospital or police station after an arrest. This test is referred to as a post-arrest breath test.

PAS breath tests

You will be asked to take a PAS test during a drunk-driving investigation. It happens after being stopped at a sobriety checkpoint or a traffic stop, but before being arrested. The test is typically administered on breath testing hand-held equipment like a breathalyzer device. Most motorists aren’t required to submit to a PAS test. You can freely refuse to take the test. However, some drivers don’t have the option of declining this test. They include those motorists that are presently on probation for DUI and underage drivers who are under investigation for underage DUI.

If you are on probation or are an underage driver (under 21 years), refusing to submit to a preliminary alcohol screening test is deemed an offense. This offense may lead to a mandatory suspension of your driver’s license irrespective of whether you are ultimately convicted of DUI or not.

To any other driver, the preliminary alcohol screening test is considered a field sobriety test. It only helps the arresting officer to decide whether or not he/she has to arrest you for DUI. There’s no punishment for declining to submit to a preliminary alcohol screening test if you are 21 years and above or are not on probation for DUI.

Post-DUI breath test

In California, in case you have a privilege to drive, then you have given consent to submit to a breath or blood test after a DUI arrest. This is according to the implied consent law. Therefore, taking chemical tests is a must for all motorists who have legally been put under arrest for drunk-driving. This is the case even if you already did a PAS test. Motorists may choose to have a blood or breath test after an arrest. However, there are instances where you don’t have the freedom to select the test you wish to take. They include when:

  • The arresting officer has a reason to believe you were driving while intoxicated with drugs. In this case, you will be required to take a DUI blood test
  • You are incapable of blowing hard enough into the breathalyzer to do a breath test
  • You are unconscious
  • Because you needed medical attention, you were transported to a healthcare facility where there is no equipment to perform a breath test

Refusing to submit to a DUI test after an arrest has its repercussions. The consequences include a one-year driver’s license suspension and a compulsory jail sentence enhancement of forty-eight hours if convicted of drunk-driving. However, you can always decline to submit to a DUI breath test in case you have chosen to do a blood DUI test.

Additionally, refusing the test will not allow you to get a restricted driver’s license at any period during your suspension. The prosecution can also use your refusal in arguing that it shows consciousness of being guilty and that if you had agreed to the test, your BAC would have been 0.08%.

Fighting refusal charges

You may be able to challenge the refusal charges against you by arguing the following defenses:

  • The arresting officer didn’t give a proper warning about what the repercussions of refusing to agree to chemical tests would be. Under VC 23612, the officer should notify you about the consequences you will face for refusing a test after an arrest. Failure to which, you cannot be punished for refusing the test.
  • You were unlawfully arrested
  • You were incapable of hearing or comprehending the warning and, therefore, couldn’t give meaningful consent. This defense works better in cases where drugs or alcohol are not the reason for your deafness or not being able to understand the warning.
  • You were incapable of completing the test due to a physical condition, and the inability wasn’t willful or intentional. You can also argue that the officer did not allow you to take an alternative test. However, in case you were given another test and declined, it would still be deemed as a refusal. In case you’re incapacitated due to a bodily injury like epilepsy, head trauma, etc., you will be excused for failing to take a breath test. And if you are physically incapable of taking the test, the officer may request that you do a blood test. Refusing to agree to a blood test is still an offense and may lead to license suspension. Note that you being incapacitated is not a matter of choice. For instance, you cannot refuse a chemical test because you decide you’re too intoxicated. But in case you were unconscious due to drinking a lot of alcohol, then that does not qualify as a refusal.
  • The officer unlawfully coerced you to agree to a breath test against your consent.

DUI attorneys have not reached any consensus on which between a blood test or breath test is the best. The primary benefit of DUI breath tests is: it is non-invasive and quick. However, these tests are subject to errors. These errors may often lead to falsely high blood alcohol concentration (BAC) results. The main benefit of a DUI blood is: a blood sample can be divided into two portions, and one portion saved for later use. For example, the saved blood sample can be availed to you for independent and separate retesting through blood split motions.

Breath samples cannot be preserved, as is the case with blood samples. Therefore, you cannot conduct distinct and independent testing, later on, to verify how accurate the original test was. However, what is crucial is not what test you choose to do, but whether or not the arresting officer complied with the right procedure as per Title 17.

Title 17 Regulations and How They Apply to Breath Tests

Title 17 regulations set forth procedures to follow during a drunk-driving chemical testing.  Police officers and laboratories have to adhere to these procedures any time they gather and process breath samples. Failure to follow the process, BAC results can be compromised.  A skilled attorney can use the mistakes in the BAC results to fight DUI charges.

The initial step in using the compromised BAC results against the prosecution is filing a motion seeking to strike off the proof (PC 1538.5). If the court grants this motion, the results of the test will be rendered inadmissible. This means that the evidence of your BAC will not be there. This often leads to a plea bargain, and in other cases, a complete dismissal of one’s charges.

There are several rules for drunk-driving chemical tests provided under Title 17. The most critical ones are:

  • The breath testing equipment should be maintained in an excellent working condition
  • The device should be calibrated after every 150 uses or ten days, whichever comes first
  • The individual administering the test should be well-trained about the specific equipment used
  • The motorist has to be continuously observed for fifteen minutes before the breath testing. During this fifteen minutes duration, the driver must not:
  • Drink, eat or place anything in their mouth
  • Regurgitate, vomit, or burp. This may bring stomach alcohol to the mouth
  • Smoke
  • The breath test administrator must draw the air he/she is testing from deep into the lungs
  • The breath test operator has to get two samples of the breath, which shouldn’t differ from one another by over .02g/100ml of blood alcohol (for this, you may be required to blow more than twice into the breathalyzer)
  • The laboratory analyzing the breath sample has to keep comprehensive records of device calibration, test results, and personnel.

Violations of Title 17 regulations that can result in falsely high BAC results are categorized into three main groups:

  • equipment that wasn’t correctly calibrated or tested
  • Operator error
  • Failure to maintain records as California law requires

A skilled DUI attorney will obtain laboratory and police records to fish out these mistakes. Also, he/she will be scrutinizing these records to find out whether or not the administrator of the test did the following:

  • Checked to ensure the motorist’s had not put anything in the mouth
  • Observed the motorist continuously for fifteen minutes before giving the test
  • Recorded when the fifteen-minute period began
  • Correctly fixed the mouthpiece and the machine
  • Recorded when each blow into the breathalyzer was made

The Science of Breath Testing

Deep Lung (alveolar) air

Breath test devices measure the alcohol quantity in alveolar. Alveoli are sacs (balloon-like) found deep in the lungs. These sacs are bordered by capillaries, fine blood vessels (not more than 0.001mm thick).  Capillaries are slender enough to allow oxygen to pass from the lungs to the blood. Similarly, they allow carbon dioxide as well as other wastes like alcohol from the blood to move to the alveoli. That is why; the law dictates that breath test samples should be drawn from the alveoli.

How a Breath Testing Device Measures Alveolar Air

To help you understand how breath tests work, you must first understand the order by which the air exits the lungs when you breathe. The order is as follows: From the lungs to the throat & upper airway, then to the nasal/mouth area.

Since the alveolar is the deeply located organ, alveolar air leaves your lungs the last. Also, it is where the highest concentration of alcohol is. Therefore, to get accurate results, a driver is requested to blow very hard during the DUI breath testing. 

Not every driver can blow hard enough to obtain reliable test results. People with health conditions affecting their lungs, as well as older people may find it hard to generate the amount of air needed for testing.

Partition ratios

Breath tests don’t directly measure BAC as blood tests do. The testing equipment measures the alcohol found in alveolar air, then mathematically converts that amount into a roughly equal blood alcohol concentration. The conversion element used is called partition ratio. This partition ratio reflects the relationship that exists between breath alcohol and blood alcohol. Under California law, the partition ratio used in breath-testing devices is set at 2100:1. By this, it means that the quantity of alcohol found in 2100 ml of breath is presumed to be equal to the alcohol amount found in 1ml of blood.

How Partition Ratio May Cause False BAC Results

Going by the law, the partition ratio is unchanging (fixed at the ratio of 2100:1). However, people’s lungs take up alcohol from their blood at different rates. This implies that partition ratios may vary broadly both for one person at separate times and across the population. However, in VC 23152b cases, that is, operating a vehicle with a .08% or more BAC, this does not matter. The legislature set the 0.08% limit and the 2100:1 ratio. Therefore, a driver who has a BAC of 0.08% or more on breath testing equipment that has a partition ratio of 2100:1 is considered legally intoxicated. It doesn’t matter whether the driver is actually impaired or not.

The rationale behind partition ratios could also help you fight VC 23152a DUI charges.  VC 23152a charges require the prosecuting attorney to show that you were impaired. This can help in cases like when your BAC is at 0.07% or 0.06%. When merged with other proof like physical intoxication signs, poor results of field sobriety tests, or traffic violations, it can get you a conviction. However, if your partition ratio wasn’t 2100:1, you BAC may not be marginal. Once your DUI defense attorney explains this in court, it may be enough to cast reasonable doubt that you were driving while impaired.

Health Conditions and Diet Can Also Affect Breath Test Readings

Certain health conditions or diets can trigger a breathalyzer device into recording falsely elevated BAC results. The conditions include:

  • Diabetes
  • Low carbs/ high protein diets
  • Gastrointestinal reflux disease (GERD)


GERD is a chronic digestive disease. Other conditions include acid reflux and heartburn. These conditions can lead to falsely elevated BAC readings after a breath test. For people suffering from these conditions, the contents of the stomach sometimes move back to the mouth.  When this happens, breathalyzer devices can detect stomach acid in these contents as alcohol.

Low carbs/high protein diets

Diets containing low carbohydrates or high proteins can also trick breathalyzer devices. Popular kinds of diets that may lead to false BAC results include Zone, Whole 30, South Beach, and Atkins diets. When you consume these diets, your body is forced to utilize stored fats as a source of energy rather than glucose. This process leads to the creation of ketones as a by-product. Ketones are the same as acetone in terms of the chemicals they contain.

Most breath testing equipment cannot validly differentiate between ethyl (alcohol in alcoholic drinks) and acetone alcohol.  Therefore, these diets trick the machine into detecting ketones as ethyl.

Hypoglycemia or diabetes

Diabetes can also cause falsely high BAC results on breath tests. This happens because the livers of people who have diabetes often generate ketones. As we said earlier, ketones are chemically the same as the alcohol found in alcoholic drinks. Diabetes patients have difficulty producing insulin, a hormone that assists one’s body to burn glucose to produce energy. Thus, these patients are forced to burn stored fats to generate energy. And as we said earlier, when stored fats are burnt, ketones are the by-product. A portion of ketones finds their way into the breath, which can trick a breath testing device.

It is crucial that, if you are arrested for DUI, you let your attorney know about all your health conditions and the dietary problems even if it’s not relevant. An expert attorney would understand whether and when a health condition can be used as a defense strategy. It may be the way out of keeping you from a wrongful conviction based on incorrect breath test readings.

Residual Mouth Alcohol and its Effect on Breath Test Results

After you take an alcoholic drink, a small amount of alcohol is left in your mouth. The remaining amount is what is called residual mouth alcohol. A breath test requires you to blow hard enough into the breathalyzer so you can generate alveoli air for a breath sample. However, as the breath exits via your mouth, it moves along with any residual alcohol.

Mouth alcohol can stay in your mouth for about fifteen to twenty minutes. Therefore, even if there is a slight quantity of residual mouth alcohol, it will appear in a breath sample.

What causes mouth alcohol?

Factors that can result in mouth alcohol may include:

  • Cough syrup
  • Breath sprays and mouthwashes that have alcoholic content in them
  • A recently consumed alcoholic beverage even if it doesn’t have enough alcohol to make you legally drunk

In most cases, mouth alcohol disappears after 15 to 20 minutes. It is for this reason that Title 17 procedures require fifteen minutes of continuous observation before commencing a breath test. In case the test is conducted soon after arrest, or if you consume any alcoholic beverage during this period, it could lead to falsely elevated BAC results.

Other Contributing Factors to Falsely Elevated BAC results

Breath testing devices have been advanced to produce better results. However, there are still other elements that may, under given circumstances, cause these devices to generate falsely high results. They include:

Inhaled chemicals like acetone

Even though it rarely happens, BAC may sometimes be inflated falsely in individuals who work in an environment surrounded by volatile compounds like acetone. If you inhale these volatile chemicals, they may be detected by DUI breath testing equipment as alcohol.

Rising levels of blood alcohol

After consuming alcohol, the levels of alcohol in the blood continue to increase for thirty to forty-five minutes. In certain cases, the rising can go for two hours for the alcoholic drink to be wholly absorbed in the bloodstream. An arrest and investigation may happen within this time. This implies that by the time you take a breath test, the levels of alcohol in the blood may be quite higher as compared to when you were operating the car.

An expert DUI witness may be able to back out your BAC, which may indicate that you were arrested when your blood alcohol concentration was still rising.

Consult a San Jose Criminal Defense Attorney Near Me

If you have been arrested for DUI, you should contact an experienced DUI attorney as soon as possible. There might be a chance that you have been wrongfully accused based on the chemical test results. Not only can the results be faulty, the arresting officer might also have committed mistakes during the arrest that can render the whole case baseless. If you hire a skilled lawyer, he/she may be able to unearth these mistakes and have your case dismissed. For San Jose residents, call the San Jose DUI Attorney Law Firm at 408-777-6630, and we will get started on your case right away.