Table 1 Percentages of Drivers with THC Positivity in Blood and Oral Fluid and Sensitivity-Specificity Analysis of the Oral Fluid Test using the Blood Test as the Reference Criterion. The Analyses were performed for All Drivers and Stratified by Driver’s Characteristics
| Â | N | Positivity in blood THC N (%) | Positivity in oral fluid THC N (%) | Sensitivity % (95% CI) | Specificity % (95% CI) |
|---|---|---|---|---|---|
All | 4596 | 431 (9.4) | 411 (8.9) | 79.4 (75.2, 83.1) | 98.3 (97.9, 98.7) |
Age (years) | |||||
 16–20 | 479 | 76 (15.9) | 75 (15.7) | 81.6 (71.0, 89.6) | 96.8 (94.6, 98.3) |
 21–34 | 1909 | 241 (12.6) | 233 (12.2) | 80.1 (74.5, 84.9) | 97.6 (96.8, 98.3) |
 35–54 | 1491 | 92 (6.2) | 88 (5.9) | 81.5 (72.1, 88.9) | 99.1 (98.4, 99.5) |
  ≥ 55 | 717 | 22 (3.1) | 15 (2.1) | 54.6 (32.2, 75.6) | 99.6 (98.7, 99.9) |
Gender a | |||||
 Female | 1980 | 143 (7.2) | 128 (6.5) | 74.1 (66.1, 81.1) | 98.8 (98.2, 99.3) |
 Male | 2597 | 282 (10.9) | 279 (10.7) | 82.3 (77.3, 86.5) | 98.0 (97.3, 98.5) |
Race | |||||
 White | 2718 | 186 (6.8) | 173 (6.4) | 74.7 (67.9, 80.8) | 98.7 (98.1, 99.1) |
 Black | 1015 | 181 (17.8) | 182 (17.9) | 86.7 (80.9, 91.3) | 97.0 (95.6, 98.0) |
 Other | 863 | 64 (7.4) | 56 (6.5) | 71.9 (59.2, 82.4) | 98.8 (97.7, 99.4) |
Last time use of marijuana b | |||||
 Beyond a year/Never | 3651 | 106 (2.9) | 107 (2.9) | 72.6 (63.1, 80.9) | 99.2 (98.8, 99.4) |
 Over a month | 294 | 51 (17.3) | 50 (17.0) | 84.3 (71.4, 93.0) | 97.1 (94.2, 98.8) |
 Past month/2 days | 279 | 98 (35.1) | 87 (31.2) | 77.6 (68.0, 85.4) | 93.9 (89.4, 96.9) |
 Past 24 h | 209 | 158 (75.6) | 148 (70.8) | 82.9 (76.1, 88.4) | 66.7 (52.1, 79.2) |
Blood alcohol concentration (ng/dl) | |||||
 0 | 4485 | 405 (9.0) | 379 (8.5) | 78.3 (73.9, 82.2) | 98.5 (98.1, 98.8) |
 1–39 | 34 | 12 (35.3) | 14 (41.2) | 100.0 (73.5, 100) | 90.9 (70.8, 98.9) |
 40+ | 77 | 14 (18.2) | 18 (23.4) | 92.9 (66.1, 99.8) | 92.1 (82.4, 97.4) |