1. Avoid smoking or vaping on the day of the test, write down the time of last consumption

2. Avoid using chest-restrictive garments (vests, corsets or very tight clothing)

3. It is not necessary to suspend basic medication

4. Fasting is not required for the test, light eating is recommended

5. Avoid intense exercise, at least four hours before (if the patient has exercised, it is necessary to specify it)

6. Do not use supplemental oxygen for ≥ 10 minutes, if the patient’s clinical status allows it

7. Avoid consuming alcohol on the day of the test

8. If a nitrogen flushing test must also be performed, it is recommended that the carbon monoxide diffusion test be performed first; If carried out later, wait twice as long as the duration of the nitrogen flushing test2

9. In case of suspicion of high COHb levels (smokers, firefighters, etc.), it is recommended to measure them18,24

10. It is recommended to apply a brief medical history questionnaire, which includes:

a. History of current or past smoking and vaping, total number of years of smoking, and average daily number of cigarettes per day

b. History of occupational exposure to fumes or dusts, total number of years of exposure and average hours per day

c. History of respiratory symptoms: dyspnea, wheezing, cough, and expectoration

d. Contraindications of the test: acute cardiovascular disease, acute or active respiratory infections (influenza, common cold, tuberculosis, etc.), advanced or complicated pregnancy