When someone is charged in California with driving under the influence (DUI), the prosecution usually relies on the results of one or more DUI tests. Presumably, these tests are “scientific,” and the results are considered conclusive evidence of a DUI defendant’s guilt or innocence.

But are the various DUI tests genuinely scientific or even reliable? Can a DUI defense attorney challenge DUI test results?

WHAT DUI TESTS ARE USED IN CALIFORNIA?

Law enforcement officers in California administer three different types of DUI tests:

1. field sobriety tests (FSTs)
2. preliminary alcohol screening (PAS) tests
3. chemical DUI tests

FSTs and PAS tests are typically requested when a police officer suspects that a motorist is driving while intoxicated. An arrest for DUI can be made – and usually is made – on the basis of these test results.

A chemical DUI test is typically conducted after an arrest for DUI. If the chemical breath, blood, or urine test measures a motorist’s blood alcohol content (BAC) level at or above 0.08 percent, that is the test result that a prosecutor will use as evidence.

WHAT’S THE FIRST THING YOU MUST DO IF YOU ARE ARRESTED FOR DUI?

If you are arrested and charged with DUI on the basis of any DUI test in Orange County or elsewhere in southern California, reach out at once to a skilled DUI lawyer. You will need sound legal advice and aggressive defense representation – immediately.

Keep reading, because what follows is a brief explanation of the various DUI tests and the role they play in a DUI prosecution in California.

WHAT ARE FIELD SOBRIETY TESTS AND WHY ARE THEY UNRELIABLE?

Before making an arrest for driving under the influence, a police officer may ask a motorist to take one or more field sobriety tests. The most commonly used FSTs are:

1. The walk-and-turn: The driver is asked to walk a straight line, turn around, and walk back.

2. The one-leg stand: The driver is asked to stand on one leg, firmly, without wobbling.

3. The horizontal gaze nystagmus (or “HGN” test): The driver is asked to follow an object with his or her eyes so that the eye movements may be observed.

Even though FSTs are used almost universally by law enforcement agencies, they are admittedly subjective and subject to all types of influences.

Even a sober motorist may appear impaired due to exhaustion, nerves, and a number of medical conditions.

WHAT IS A PAS TEST? ARE YOU REQUIRED TO TAKE FSTS AND PAS TESTS?

The police may also request a motorist to take a preliminary alcohol screening (PAS) test using a handheld breathalyzer device. Handheld breathalyzers, however, are unreliable and often inaccurate.

Motorists who are age 21 or older in California should pass on the PAS test and the FSTs. You have the right to decline – politely – to take any of these tests when you’ve been stopped for suspicion of DUI, and most California DUI attorneys would recommend not taking the tests.

However, if you are below age 21 or if you’re serving probation for a prior DUI conviction, you must submit to a PAS test or FST if requested by a police officer.

But unless you are below 21 or on DUI probation, you’re not required to take a DUI test until and unless you’ve been arrested for DUI.

HOW DOES EVERYTHING CHANGE IF YOU’RE PLACED UNDER ARREST?

Everything changes, however, if you are placed under arrest for DUI. At that point, you are obligated by law to take a chemical DUI breath, blood, or urine test.

California law presumes “implied consent.”

This means that drivers who have been formally and legally arrested for DUI have already “consented” – by law – to a chemical DUI test simply by acquiring a California driver’s license. Drivers with out-of-state licenses imply consent simply by driving in California.

WHAT IS THE PENALTY IF YOU REFUSE TO TEST AFTER BEING ARRESTED?

If you refuse to submit to a chemical DUI test after you’ve been arrested for DUI:

1. Your driver’s license can be suspended for a year whether or not you are eventually convicted of DUI.

2. An additional 48 hours in jail and six months of DUI classes can be added to your sentence if you are convicted of the DUI charge.

WHAT’S THE PROBLEM WITH BREATHALYZERS?

How will a good DUI attorney challenge the results of chemical DUI tests?

The biggest problem with breathalyzers is that they will return false positive readings from anything that chemically resembles alcohol, including a variety of foods, medicines, and non-alcoholic beverages.

Colognes, perfumes, and even breath fresheners can show up as alcohol on a breathalyzer test, and anyone who suffers from gastroesophageal reflux disease, diabetes, or hypoglycemia could be wrongly accused of DUI on the basis of an inaccurate breathalyzer test result.

Your DUI attorney may dispute the results of a breathalyzer test by asking – and getting the answers to – these questions:

1. Was the test administered properly?
2. Was the officer who conducted the test trained properly?
3. Was the breathalyzer itself calibrated and maintained properly?

WHAT PROBLEMS ARE ASSOCIATED WITH BLOOD TESTS AND SAMPLES?

If the police took a blood sample from you for testing, your attorney might question the qualifications and training of the police officer who drew your blood. If that person wasn’t properly trained and qualified, it’s possible that the blood test results could be thrown out.

Your DUI lawyer might also question a blood sample’s “chain” of custody. If a blood sample is introduced as evidence, the state must also provide a list of those who had custody of the blood sample.

If any gaps are in that custody chain, the blood sample could have been tampered with or contaminated, so your lawyer may ask the court to exclude the test results for that reason.

Urine tests are rare for DUI, but when they are used, as you might imagine, the test must be conducted according to strict guidelines.

WHAT PROBLEMS CAN EMERGE AT THE TESTING LABS?

Laboratory equipment may also come under your attorney’s scrutiny, and in some incidents, laboratories and their personnel have been guilty of negligence, failing to maintain lab equipment or to handle samples properly.

If there is even a hint of negligence suggesting that a lab mishandled your blood or urine sample, your DUI lawyer will investigate the laboratory and find out the facts.

If you are charged with driving under the influence in southern California, don’t let the results of any DUI test dishearten you. That test result can probably be challenged.

Contact an experienced Orange County DUI lawyer as quickly as possible after a DUI arrest, and let that attorney advocate aggressively on your behalf for justice. You have that right.