Table 3 Characteristics of study participants

Age, years, median (IQR)

26.5 (23.6–28.0)

25.7 (23.4–27.7)

27.2 (25.3–28.9)

26.3 (23.7–28.2)

Gender

Females, N (%)

32 (46%)

24 (62%)

4 (29%)

4 (25%)

Race

White, N (%)

55 (80%)

30 (77%)

11 (79%)

14 (88%)

Non-White, N (%)

14 (20%)

9 (23%)

3 (21%)

2 (13%)

Smoking

Former, N (%)

–

–

11 (79%)

–

Current, N (%)

–

–

–

26 (100%)

Never, N (%)

–

43 (100%)

3 (21%)

–

Years of smoking, median (IQR)

–

–

6.5 (4.3–10.0)^a

9.5 (4.0–10.0)

Pack Years, median (IQR)

–

–

3.7 (0.8–7.7)^a

6.8 (2.9–10.0)

Cigarettes per day, median (IQR)

–

–

15 (2.8–20.0)^a

20.0 (10.0–20.0)

Days since last cigarettes, median (IQR)

–

–

737.0 (316.5–1125.0)^a

–

Electronic cigarette (EC) use

Years of EC use, median (IQR)

–

–

3.0 (2.0–3.3)

–

Puffs per day, median (IQR)

–

–

100.0 (28.8–200.0)

–

EC–liquid (ml) per day, median (IQR)

–

–

9.0 (5.0–10.0)

–

Nicotine (mg/ml), median (IQR)

–

–

6.0 (3.0–13.5)

–

Urinary biomarkers*

–

Nicotine equivalent (nmol/mg Cr), median (IQR)

–

0.003 (0.001–0.006)

12.1 (4.3–35.6)

19.5 (6.6–43.5)

Nicotelline (ng/mL), median (IQR)

–

–

2.0 (2.0–23.0)

1011.2 (124.2–1274.8)

Anatabine (ng/mL), median (IQR)

–

0.1 (0.1–0.1)

0.1 (0.1–2.0)

8.5 (2.5–19.8)

NNAL (pg/mg Cr), median (IQR)

–

0.5 (0.2–0.9)

12.4 (1.2–35.3)

278.1 (126.1–505.3)

Propylene glycol (mg/mL), median (IQR)

–

2.0 (0.9–5.0)

27.9 (5.5–54.2)

6.6 (2.7–20.8)