Failure to draw blood means that the patient’s blood cannot be obtained properly for clinical blood sampling and testing. There are many reasons why blood can’t be drawn out, common reasons are patients with severe failure, such as long-term severe infection, insufficient blood volume, hypovolemic shock patients, due to insufficient blood volume, poor vascular filling, when the bleeding often appear the phenomenon of blood can’t be drawn out. When the patient’s shock symptoms improve, the blood volume is replenished and the blood vessels are filled, then it is easier to draw blood. It can also be seen in patients with abnormally high lipid levels, because the viscosity of blood is significantly higher in patients with high lipid levels, and blood clots occur in the thinner blood vessels when blood is drawn, resulting in obstruction of the needle and making it difficult to draw blood. So there are various reasons why blood cannot be drawn, and specific measures need to be found according to the different reasons.