Evaluation of the post-rotational nystagmus test (PRN) in determining alcohol intoxication

This study evaluated the accuracy of the post-rotational nystagmus test (PRN) on the basis of the results of 1006 PRN tests performed at the Institute for Forensic Medicine in Ljubljana between 1998 and 2002 during standardized medical examinations in cases of suspected drunk driving. The evaluation of PRN test results with blood alcohol concentration (BAC) as a reference was based on classification into the following categories and characteristics: true positives (TP), true negatives (TN), false positives (FP), false negatives (FN), sensitivity, specificity, positive predictive values (PPV), negative predictive values (NPV), and accuracy. An optimal cut-off value of 10 s for post-rotational nystagmus time was chosen with the help of a receiver operating characteristic (ROC) curve for the BAC limit of 0.5 g/kg. The results of the decision analyses were: TP = 584, FP = 43, FN = 229, TN = 150, sensitivity = 0.718, specificity = 0.777, PPV= 0.931, NPV= 0.396, and accuracy = 0.730. The area under the ROC curve (AUC) was 0.813. Based on the AUC, the post-rotational nystagmus test is a good test for predicting alcohol intoxication over 0.5 g/kg. As a part of the physician's examination, it contributes significantly to the description of the clinical state.