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Iowa DUI breath tests explained


Preliminary screening test in Iowa OWI (DUI) meets a threshold question. It is not a confirmatory test.

One of the most confusing things about a drunk driving investigation in Iowa is that there are two and sometimes three breath tests during the course of your interaction with law enforcement.

Following the Standardized Field Sobriety Tests, or, SFSTS—which include the Horizontal Gaze Nystagmus (HGN) test, Walk and Turn (WAT), and One Leg Stand (OLS)—a law enforcement officer who has established “reasonable grounds” to believe someone is in violation of Iowa’s drunk driving statute may request a preliminary screening test. This is not the final breath test. Law enforcement officers investing DUI cases in Iowa almost always call this by its shorthand in the field: PBT, or preliminary breath test.

Some law enforcement officers, including the Department of Public Safety department that is responsible for maintaining and certifying both the evidentiary Datamaster DMT testing machines and the preliminary breath testing machines, have started calling it a “portable breath test."


The Iowa Department of Public Safety has approved over a dozen preliminary screening test tools for law enforcement. Image: from Iowa DPS website

The preliminary screening test is a field breath test the results of which are not admissible before the jury on the issue of intoxication in an OWI prosecution. It may be used by law enforcement, however, to prove to the judge in a pretrial challenge to an arrest or further testing that the officer had reasonable grounds to invoke implied consent and request an arguably more reliable, admissible evidentiary chemical test at the stationhouse—that can include a Datamaster DMT evidentiary breath test, a urine test, blood test, or combination of some or all three.

Iowa Code § 321J.5 states that an officer who has reasonable grounds to believe that a motorist is under the influence may further seek a preliminary screening test but that the test results of this breath test in the field “shall not be used in any court action except to prove that a chemical test was properly requested.”

In this way, the preliminary screening test in the law is merely a precursor to evidentiary testing that the law identifies as evidentiary “chemical” testing to Iowa Code §§ 321J.5 and 321J.6.

Officers who call the preliminary screening test a PBT or portable breath test gloss over its legal significance as a merely preliminary screening tool and not an evidentiary test.



The law is clear: preliminary screening tests are not merely portable, confirmatory tests for officers sure of their testing. They have legal significance and may be challenged.

While some will tell OWI test subjects that the test is "not admissible," they ignore nuance that the officer must be prepared to prove to the judge that overall grounds to invoke implied consent and request chemical testing were reasonable-- including the result of the preliminary screening test-- before a trial ever occurs. Moreover, notwithstanding officers’ confirmation bias, the preliminary screening test does not merely tell them what they already know to be true. It is a legal hurdle that they must overcome in order to restrain the freedom of a motorist further for chemical testing at the stationhouse.

While it may seem like a convenient shorthand to trade “portable” for “preliminary,” it is important to note that “preliminary” carries with it the very important, necessary, and legal meaning that “portable” just does not convey. It is also extremely important to emphasize that the test is a "screening" test meaning that it is just one hurdle an officer must clear to continue the investigation.

Some of this "portable" versus "preliminary" language appears lost on legislators attempting to amend the code to make screening tests more admissible. A few years ago an Iowa legislator proposed a bill that codified "portable" testing for admission at jury trial. Although the bill did not advance, it is sure to reappear in similar form as law enforcement proponents seek to use as evidence what was intended only as a screening tool in the field, arguing that advances in technology, not legal protections, should drive any changes to the law.


If you or a loved one have been arrested for Operating While Intoxicated, or, OWI (sometimes called DUI in other states) in Cedar Rapids, Iowa City, or other Iowa community, contact us for a free initial consultation. However, remember that a blog is not legal advice and that no attorney-client relationship is established by sending unsolicited information to an attorney over the Internet.

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