There are several reasons why the blood drawn is purple: 1. If the blood drawn is from a vein, the blood drawn is purple, sometimes darker in color, and even looks black is a normal phenomenon. Because the venous blood itself contains less oxygen, and contains a lot of carbon dioxide, oxygenated hemoglobin content is less, oxygen and hemoglobin color is bright red, venous blood purple belongs to the normal phenomenon. The blood of some people is more viscous, the degree of purple is heavier, some people are less viscous, the degree of purple is lighter, there is no significant difference and no meaning. 2, if the blood drawn is arterial blood and purple, it proves that the whole body has a lack of oxygen, to check whether there is lung disease, asthma or blood circulation disorders and other problems, the general arterial blood should be bright red, because It contains a large amount of oxygenated hemoglobin and no carbon dioxide or a relatively low concentration.