…and Testing Practices in Fatal Crashes
by the U.S. Dept. of Transportation
National Highway Traffic Safety Administration
There is no consistent policy or set of procedures between, or sometimes even within, States for drug testing. Considerable variation exists regarding who is tested; which drug is tested for; type of test, cut-off levels, and equipment; and which biological specimen (blood, urine, or oral fluid) is used.
Jurisdictions (or labs within a jurisdiction) may vary also regarding the sensitivity of their tests and their “cut-off” levels for indicating the presence of a drug. Testing for drugs involves performing screening tests (which are less expensive and less sensitive), and confirmatory tests. Some laboratories do not consistently perform both types of tests, even when they are appropriate.
Caution should be exercised in assuming that drug presence implies driver impairment. Drug tests do not necessarily indicate current impairment. Also, in some cases, drug presence can be detected for a period of days or weeks after ingestion….
These facts, plus the information presented above, demonstrate that we cannot infer whether drugged driving has increased; similarly we cannot know the extent to which drugged driving differs across States.