There are no clear rules about smoking before a blood draw, but it is usually recommended that patients abstain from smoking 1 day (i.e., 24 hours) before the blood draw. The effect of smoking on the body is a long-term chronic process. Long-term smoking has a certain effect on blood tests such as routine blood and blood gas analysis, while occasional smoking does not usually have a significant effect on the test results. However, to ensure that the test results are not affected by smoking, try to abstain from smoking 1 day prior to the blood draw. The carbon monoxide hemoglobin level in long-term smokers can reach 8%, while the level in nonsmokers is below 1%, and their catecholamines and serum cortisone concentrations are also higher than in nonsmokers. The blood leukocyte count will be increased, higher than non-smokers by 30%, with decreased eosinophils, increased neutrophils and monocytes, and high average red blood cell volume. In addition, a few days before the blood draw, patients should maintain a balanced diet and good lifestyle habits, starting fasting after 8:00 p.m. 1 day before, and should not exercise strenuously before the blood draw.