ANALYSIS OF AGREEMENT BETWEEN EXPIRED-AIR CARBON MONOXIDE MONITORS.

INTRODUCTION: The current study examined the level of agreement in expired-air carbon monoxide (CO) values, focusing especially on those confirming abstinence, between the two most commonly used CO monitors, the Vitalograph BreathCO and the Bedfont piCO+ Smokerlyzer.

METHODS: Expired-air samples were collected via both monitors from adult dependent smokers (44 M, 34 F) participating in studies using CO values to confirm abstinence durations of: 24 hours, 12 hours, or no abstinence. All met DSM-IV nicotine dependence criteria and had a mean (SD) Fagerström Test of Cigarette Dependence score of 5.1 (1.8). Paired data collected across multiple visits were analyzed by regression-based Bland-Altman method of Limits of Agreement.

FINDINGS: Analysis indicated a lack of agreement in CO measurement between monitors. Overall, the Bedfont monitor gave mean (±SEM) readings 3.83 (±.23) ppm higher than the Vitalograph monitor. Mean differences between monitors were larger for those ad lib smoking (5.65±.38 ppm) than those abstaining 12-24 hours (1.71±.13 ppm). Yet, there also was not consistent agreement in classification of 24 hour abstinence between monitors.

CONCLUSIONS: Systematic differences in CO readings demonstrate these two very common monitors may not result in interchangeable values, and reported outcomes in smoking research based on CO values may depend on the monitor used.