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BAC testing in DUI cases does not rely on a single type of test. Instead, DUI enforcement typically uses two distinct categories of alcohol testing: screening tests and evidentiary tests. While both involve measuring alcohol presence, they serve different purposes within the enforcement and legal process.
This article clarifies the difference between screening and evidentiary BAC tests and explains how each fits into the process used to measure alcohol levels under DUI laws. Understanding this distinction helps explain why some tests are used early in an investigation while others carry greater legal weight later on.
What Screening Tests Are Designed to Do
Screening tests are designed to help officers quickly assess whether alcohol may be present and whether further investigation is warranted. These tests are typically used during the early stages of a DUI encounter, such as at the roadside or during an initial stop.
The purpose of a screening test is not to establish a final BAC value for legal determination. Instead, it provides a preliminary indication of alcohol consumption. Screening tests help officers decide whether additional testing should occur, but they are not intended to stand alone as definitive proof.
Because screening tests are used for assessment rather than final measurement, they prioritize speed and practicality. Their role is to inform next steps in the enforcement process rather than to conclusively determine whether a legal limit has been exceeded.
What Makes a Test Evidentiary
Evidentiary tests are designed to produce BAC results that can be formally relied upon within DUI proceedings. These tests follow stricter procedural standards and are intended to generate a documented numerical value suitable for legal evaluation.
What makes a test evidentiary is not the testing medium alone, but the conditions under which it is administered and recorded. Evidentiary tests are conducted using approved equipment, standardized procedures, and documented protocols that ensure consistency and reliability.
The results of an evidentiary test are treated as formal measurements of alcohol concentration. These results are compared directly to applicable legal BAC thresholds and can be used as a basis for determining whether per se standards have been met.
How Results Are Treated Differently
Results from screening tests and evidentiary tests are treated differently because they serve different functions. Screening test results are typically used as investigative tools rather than as final determinations of BAC.
Evidentiary test results, by contrast, are treated as substantive evidence. They are recorded, preserved, and evaluated as part of the official DUI record. These results carry greater legal significance because they are obtained under conditions designed to support reliability and review.
This distinction explains why a driver may undergo multiple tests during a single DUI investigation. An initial screening result may lead to further testing, while the evidentiary result is the one ultimately used to apply legal standards.
Why Both Types Are Used
Both screening and evidentiary tests are used because they address different needs within DUI enforcement. Screening tests allow officers to efficiently assess large numbers of drivers or quickly evaluate potential impairment without immediately engaging in formal testing procedures.
Evidentiary tests provide the level of precision and documentation required for legal application of BAC limits. Without screening tests, enforcement would be slower and less flexible. Without evidentiary tests, enforcement would lack the standardized measurements needed for consistent application of DUI laws.
Using both types together creates a layered system. Screening tests guide investigative decisions, while evidentiary tests establish formal BAC measurements. This structure allows DUI enforcement to balance efficiency with accuracy.
Summary
The difference between screening and evidentiary BAC tests lies in their purpose and legal significance. Screening tests are used to assess whether alcohol may be present and whether further investigation is needed. Evidentiary tests are used to formally measure BAC and apply legal standards.
Understanding how these tests function within the methods used to measure BAC in DUI cases helps clarify why both types exist and why they are treated differently. Together, screening and evidentiary tests form a comprehensive system for evaluating alcohol-related driving under DUI laws.