Q. What does a CO breath test show?

It shows the amount of carbon monoxide (CO ppm) in the breath, which is an indirect non-invasive measurement of the amount of carbon monoxide in the persons blood stream which is called carboxyhemoglobin (%COHb). Dependent on the level of carbon monoxide measured the person who breathed into the CO monitor can be classed as a non smoker or smoker.

Q. How does smoking elevate COHb?

In a typical puff of a cigarette smoke there is about 5% CO by volume. Carbon monoxide actively competes with oxygen to bind to the red blood cells in the blood stream (carbon monoxide has approximately 250 times greater affinity to haemoglobin in red blood cells than oxygen) when carbon monoxide binds with the red blood cells it forms carboxyhaemoglobin (COHb)). This will eventually be excreted via the lungs; the same way it went into the body.

Q. How quickly does the CO disappear from the body after smoking stops?

It takes approximately 5 to 6 hours to reduce the original level of carbon monoxide by half. Usually after a maximum period of 48 hours the ex-smoker would show the level of a non-smoker living in the same environment.

Q. If a smoker cuts down, will this reduce breath CO by an equivalent amount?

Possibly not. Studies show a smoker may smoke fewer cigarettes but will require the same amount of nicotine. As a result people often change their smoking habits resulting in less cigarettes being smoked, but they smoke fewer cigarettes more aggressively with deeper inhalations and more frequent puffs on the cigarette resulting in more smoke being inhaled and more carbon monoxide entering the body.

Q. Do cigars and pipes give low readings?

No. On the contrary. An inhaled puff of pipe or cigar smoke is much more concentrated and will give surprisingly high CO ppm levels. Any form of incomplete combustion where smoke is produced will result in carbon monoxide being produced and inhaled, so any form of smoking will result in CO being absorbed into the blood stream.

Q. How hygienic is the test?

MD Diagnostics recommend the use of SafeBreath filtered cardboard mouthpieces. SafeBreath have an in-built bacterial and viral filter ensuring >99% efficacy* resulting in complete hygienic solution, this avoids cross contamination between individuals being tested and protects both patients and equipment. SafeBreath mouthpieces are single patient use and should be disposed of after the individual has been tested on the CO breath monitor.

*SafeBreath mouthpieces have been independently tested for MD Diagnostics by the Health Protection Agency


Q. What does ppm mean?

Parts Per Million. It is a unit of measure. In this case, one part carbon monoxide in one million parts air (breath).

Q. What else does breath CO show?

It acts as an indicator as to the possible level of some 4000 toxic substances in cigarette smoke, some 60 of which cause cancer.

Q. How long after a cigarette should the test by conducted?

Ideally more than 10 minutes should elapse between exhaling into the monitor and when the last cigarette was smoked.

Q. Is it necessary to hold the breath before taking a test?

It is not necessary, however clinical research has shown that an optimum period of 15 second breath hold is required to get the best correlation between the carbon monoxide level on the breath (ppm) and that in the blood stream (COHb).  Holding your breath for less than 15 seconds this will depress the breath CO reading. However the individual should be encouraged to exhale fully and completely, for as long as possible, this “end-tidal” breath sample will give a good indication of the levels of carbon monoxide.

Q. Why do non-smokers sometimes give higher than expected readings?

This could be for several reasons: A small amount of carbon monoxide is naturally produced in the body. However external sources of carbon monoxide can also be inhaled and are detected on the breath - high ambient levels of CO from urban areas as a result of industrial or car exhaust fumes. Also it is worth checking other family members and ambient levels in the home to ensure there are no causes for higher than expected CO levels as a result of faulty appliances such as fires or boilers in the home that may be causing possible chronic CO poisoning. Certain occupations may expose workers to high levels of carbon monoxide. Also some cleaning agents and paint stripping fumes contain methylene chloride (dichloromethane) and these give off carbon monoxide. Whenever using these agents ensure the area is well ventilated.