Because the usual blood test is drawn from the human vein blood, so present dark red, the human arterial blood is bright red. The oxygenation index of venous blood is only 70%-75%, while that of arterial blood is generally above 95%. Some tests require fasting and water fasting, and the blood drawn is also concentrated blood, so the color is darker red, which is normal. It does not exclude that the body will be darker red when there is a problem. The viscous blood, as doctors often say, may be related to a recent diet that is too oily or pathological factors, blood system diseases, such as increased platelets, the body is in a hypercoagulable state, etc. In short, as long as the test results are not abnormal, the dark red blood is a normal phenomenon, do not worry.