Validity of suspected alcohol and drug violations in aviation employees

In the United States, transportation employees who are suspected of using alcohol and drugs are subject to reasonable-cause testing. This study aims to assess the validity of suspected alcohol and drug violations in aviation employees.

Using reasonable-cause testing and random testing data from the Federal Aviation Administration for the years 1995-2005, we calculated the positive predictive value (PPV) and positive likelihood ratio (LR+) of suspected alcohol and drug violations. The true status of violations was based on testing results, with an alcohol violation being defined as a blood alcohol concentration of ≥0.04 mg/dl and a drug violation as a test positive for marijuana, cocaine, amphetamines, phencyclidine or opiates.

During the 11-year study period, a total of 2284 alcohol tests and 2015 drug tests were performed under the reasonable-cause testing program. The PPV was 37.7% [95% confidence interval (CI), 35.7-39.7%] for suspected alcohol violations and 12.6% (95% CI, 11.2-14.1%) for suspected drug violations. Random testing revealed an overall prevalence of 0.09% for alcohol violations and 0.6% for drug violations. The LR+ was 653.6 (95% CI, 581.7-734.3) for suspected alcohol violations and 22.5 (95% CI, 19.6-25.7) for suspected drug violations.

The discriminative power of reasonable-cause testing suggests that, despite its limited positive predictive value, physical and behavioral observation represents an efficient screening method for detecting alcohol and drug violations. The limited positive predictive value of reasonable-cause testing in aviation employees is due in part to the very low prevalence of alcohol and drug violations.