Carboxyhaemoglobin level, smoking habit, and mortality in 25 years in the Renfrew/Paisley prospective cohort study

Carole L Hart ^1*, George Davey Smith ², David Hole ¹ and Victor Hawthorne ³

¹ University of Glasgow, United Kingdom
² University of Bristol, United Kingdom
³ University of Michigan, United States

^* To whom correspondence should be addressed. E-mail: c.l.hart{at}udcf.gla.ac.uk.

Accepted 2 June 2005

Abstract

Objective: To investigate how carboxyhaemoglobin level was related to smoking habit and to assess whether carboxyhaemoglobin level was related to mortality.

Design: Prospective cohort study.

Setting: Residents of the towns of Renfrew and Paisley in Scotland.

Participants: The whole Renfrew/Paisley study, conducted between 1972 and 1976, consisted of 7048 men and 8354 women aged 45-64 years. This study was based on 3372 men and 4192 women who were screened after the measurement of carboxyhaemoglobin level was introduced about half way through the study.

Main outcome measures: Deaths from coronary heart disease (CHD), stroke, chronic obstructive pulmonary disease (COPD), lung cancer and all causes in 25 years after screening.

Results: Carboxyhaemoglobin level was related to self-reported smoking and was higher in participants who reported inhaling compared with those who reported not inhaling, for each smoking category. There were positive relationships between carboxyhaemoglobin level and all causes of mortality analysed (relative rate associated with 1 SD (2.93) increase in carboxyhaemoglobin for all causes, CHD, stroke, COPD and lung cancer were 1.26 (1.19-1.34), 1.19 (1.13-1.26), 1.19 (1.13-1.26), 1.64 (1.47-1.84) and 1.69 (1.60-1.79) respectively). Adjustment for self-reported cigarette smoking attenuated the associations but they remained relatively strong.

Conclusions: The self-reported smoking data was validated by the objective measure of carboxyhaemoglobin level. Since carboxyhaemoglobin level remained associated with mortality after adjusting for smoking, carboxyhaemoglobin seems to capture more of the "risk" associated with smoking tobacco than self-reported tobacco consumption alone. Analysing mortality by self-reported cigarette smoking will underestimate the strength of association between smoking and mortality.

Keywords: carboxyhaemoglobin, cohort studies, inhalation, mortality, smoking

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