September 2009

Testing for Carbon Monoxide in exhaled breath


The Micro CO meter rates Carbon Monoxide in exhaled breath in parts per million (ppm)

Health New Zealand Ltd has two of these machines. Supplier: MicroMedical Ltd now,

CO in exhaled breath is used for:

1)     Checking for overnight abstinence in research projects. Confirming that a smoker has not smoked in the past eight hours. Before first cigarette in the morning, when the cut off was 15 ppm: we found mean = 9.5, median 10.5 ppm, with 10% recording the maximum of 15 ppm.)1

After 1st cigarette after overnight abstinence CO mean was 14.3 ppm, median 14 ppm, maximum 23 ppm. After excluding those testing with CO = 15 ppm before first cigarette, then the remainder, after 1st cigarette, averaged 13.3, with median 14 ppm. Thus accepting only volunteers with 0-14 ppm CO excludes only half of those who have already smoked one cigarette since waking. On the other hand, setting the cutoff at 10.5 would exclude 42% of smokers with CO under 15 ppm who claim not to have smoked their first cigarette since waking.1

In short, CO is not accurate in detecting overnight abstainers, only in detecting quitters not smoking for at least 24 hours.1


2)     Testing for CO poisoning: Diagnosing excess CO inhaled (for example in a poorly ventilated room or car) in the previous few hours.

3)     Smoking cessation: Confirming a nonsmoker has not smoked in the past 8 hours. (3-6 ppm, and certainly < 10 ppm)2



Smoking status

CO ppm in exhaled breath

Heavy smokers

> 20 5 minutes later

Moderate smokers

11-20 5 minutes later

Light smokers



23: after first 4 cigarettes of the day (half hourly)1

(46 max, 5 minimum)


>3<7 and certainly under 10

Non-smokers, not exposed to second-hand tobacco smoke[1]


Breath holding for 20 seconds before blowing into the device gives a result close to alveolar CO levels, in agreement with blood measurements of blood COHb. In estimating exposure to smoke toxicants, the alveolar resting levels of CO (as per a smokelyser), can be used to indicate the depth of inhalation, and without such data, other smoking parameters such as the amount of smoke inhaled, may be misleading as a measure of exposure of the lung to inhaled gases.3

CO has a half life of 5 hours,4 suggesting a 25% fall in 2.5 hours. Hourly smoking will thus result in increasing levels of CO in exhaled breath. The ratio of exhaled CO, after versus before, is likely to be the same across cigarette brands.4

After finishing a cigarette the CO in expired air falls rapidly to the five minute mark, then slowly in the next hour. The after-cigarette reading should not be made until 5 minutes after the cigarette is finished.5

CO boost per cigarette The increase in CO from 5 minutes before to 5 minutes after finishing smoking is 8 ppm,6 but it may be less. Smoking one cigarette every half hour, CO increased by 4.3 ppm per cigarette, with no real difference between RYO and factory made cigarettes.1

Emissions In tobacco mainstream (mouth) smoke, up to 26 mg (8700 ppm) is found in the mainstream smoke (max. 1L) of a Holiday cigarette tested in HCI mode.7 (1 ppm =1.15 mg/m3 at 25degC). Of estimated mouth smoke CO, a fifth is detected in exhaled breath; 79% is retained in the body.8


1. Laugesen M, Epton M, Frampton C, Glover M, Lea RA. Hand-rolled cigarette smoking patterns compared with factory-made cigarette smoking in New Zealand men. BMC Public Health 2009;9:194.

2 McEwan A, Hajek P, McRobbie H, West R. Manual of Smoking Cessation. Addiction Press, 2006. Blackwell Publishing.

Pirogowicz I, Jezowiecka M, Pomorski M, et al. Przegl Lek. 2004; 61: 1016-9. PMID 1579428 (PubMed indexed for Medline)

3       Dunn PJ. The effects of a reduced draw resistance cigarette on human smoking parameters and alveolar CO levels. Imperial Tobacco Research Laboratory. 1978. Bates No. 402424624.

4 Jo WK, Oh JW. Evaluation of CO exposure in active smokers while smoking using breath analysis technique. Chemosphere 2003; 53: 207-16.

5       Woodman G. Wintoniuk DM, Taylor RG et al. Time course of end-expired carbon monoxide concentration is important in studies of cigarette smoking. Clin Sci (Lond) 1987; 73: 553-5.

6       Dixon M. Kochhar N. Prasad K et al. Psychopharmacology 2003; 170: 434-442.

7 Laugesen M. Fowles J. Scope for regulation of cigarette smoke toxicity according to brand differences in toxicant emissions NZMJ 15 April 2005.

8       Feng S, Plunkett SE, Lam K et al. A new method for estimating the retention of selected smoke constituents in the respiratory tract of smokers during cigarette smoking. Inhal Toxicol 2007; 19: 169-79.

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