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DWI investigations: Maximizing impairment detection

Choosing the right driver specimen – blood or breath – may be a crucial decision in some cases

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This is the fourth article in a series that focuses on tips, techniques and methods front-line officers can use to improve their intoxicated driving interdiction abilities. Click here to read part one, click here to read part two and click here to read part three.

After making the DWI arrest, the officer needs to obtain a specimen as quickly as possible. In recent years, the trend has been to obtain blood specimens. And while that option is much more accurate and retestable than breath, generally, the results are not instant. Obtaining only blood allows a lot of drug impairment to slip by undetected.

If you can obtain a breath specimen, even if it’s just using a portable/preliminary breath tester, try to do so before getting the blood. If the breath alcohol concentration (BAC) is zero or lower than is consistent with the given level of impairment, your next step needs to be calling a drug recognition expert (DRE) to conduct an evaluation – and the first step in the DRE protocol is a breath alcohol test.


There are a lot of misconceptions about DREs; chief among them being that a DRE will respond roadside and take over your investigation or conduct an on-scene evaluation. Actually, the DRE process is conducted after the arrest has been made, is done in a secure, controlled environment and takes about an hour.

A lot of officers will skip contacting a DRE with the belief that the drugs will come out in the blood toxicology, so why bother. While this is true, it is an inaccurate assumption because unlike alcohol, drugs can remain in the blood for some time without being psychoactive.

While the toxicology tells you what substances are in the body at the time blood is drawn, the DRE can tell you the drug category or categories that are psychoactive at the time of the arrest. A drug recognition assessment is important. If the offender refuses to give blood, breath or urine, the DRE’s testimony and assessment of objective observations will be the only indicator of impairment. DREs are highly trained experts who can bolster your case with their knowledge and observations, and I exceedingly recommend you use them whenever applicable.


When it comes to drug impairment, I would be remiss if I did not mention one of my all-time pet peeves about intoxication investigations: officers who administer a horizontal gaze nystagmus (HGN) test and decide someone is not intoxicated or impaired because they did not see nystagmus.

Out of the seven drug categories (CNS depressants, CNS stimulants, hallucinogens, dissociative anesthetics, narcotic analgesics, inhalants and cannabis) only three will cause HGN (depressants, inhalants and dissociative anesthetics), so by administering an HGN, you limit your chances of detecting impairment. Always administer the full battery of tests if you suspect impairment. Only then should you decide to arrest or release.

If you wish to learn more about drug impairment and how to spot it, I highly recommend taking an Advanced Roadside Impaired Driving Enforcement (ARIDE) course, which is designed to bridge the gap between the Standardized Field Sobriety Test Practitioner and the DRE.


Lastly, when it comes time to write your report, the best practice is to make sure your grammar, punctuation and spelling are correct. Write in clear, concise and cogent sentences.

If you sound smart in your report, then you’ll sound smart to defense counsel, and they will be less inclined to challenge you.

In the next article of the series, we will look at how officers can prepare for and excel at the court testimony phase of a DWI case.

Deputy James “Zack” Holley is a patrolman for a southeastern sheriff’s office in Texas. Along with a bachelor’s degree in criminal justice from Sam Houston State University, Deputy Holley holds a Master Peace Officer’s license, is a certified Drug Recognition Expert, an SFST instructor, a vehicle crash expert/reconstructionist, field training officer and firearms instructor, and has received several awards throughout his career. Deputy Holley has several hundred DWI arrests and thousands of enforcement hours under his belt.