Exhaled Carbon Monoxide Level as an Indicator of Smoking among Undergraduate Students in Bangkok Metropolis and Bangkok Metropolitan

Abstract

Measurement  of exhaled  carbon  monoxide  (eCO)  has been used to evaluate tobacco

smoking with a range of eCO  cut-off point depending on specific  populations. Early  initiation

of smoking before 20 years of age has been associated with greater consumption, longer duration

of smoking, and increased nicotine dependence, consequently, influencing smoking cessation.

This study aimed to apply eCO test as a tool for smoke free environment campaign by examining

baseline eCO  levels, the sensitivity and specificity of eCO  test, and optimal cut-off value for

smoking  assessment in  samples of the undergraduate students. Total  of 389  undergraduate

students living in Bangkok  Metropolis  and Bangkok  Metropolitan  underwent a measurement of

eCO  levels and completed questionnaire-based interview seeking demographic information and

details of exposure to tobacco smoke, smoking  habits and smoking-related  knowledge.  Active

smokers (n = 200) had significantly  higher eCO  levels than non-smokers  (n = 138) and passive

smokers (n = 51) [median (95%  CI);  9.00 (8.00, 11.00) ppm vs 3.00 (3.00, 3.00) ppm vs 2.00

(2.00, 3.00) ppm, p < 0.001],  respectively.  The eCO  level at ≥ 6 ppm was optimal cut-off value

to classify  smokers,  with sensitivity  of 76.50%  and specificity  of 96.38%.  When  excluding  data

of smokers with > 6-hour  since last cigarette, sensitivity  increased  to 84.12%.  Obviously, active

smokers who desired to quit smoking (n = 123) had a significantly  higher awareness scores than

those who did not (n = 73) (4.02 ± 0.95 vs 3.14 ± 1.31, p < 0.001). In conclusion, eCO test with

optimal cut-off at ≥ 6 ppm is an effective tool to validate smoking  status among undergraduate

students and raise  the student’s  awareness  on adverse  effect of smoking.  The  reliability   of test

increased if an individual smoked with  ≤ 6-hour  prior to test.