If the blood vessels are too thin to draw blood, the blood can be collected by replacing other blood vessels, such as the thicker veins like the cephalic vein and the noble vein. If the above two veins are still unable to collect blood, it is recommended that the blood can be collected from the vein on the back of the foot or the beginning of the saphenous vein, as this vein is thicker and it is easy to collect the required venous blood. If venous blood cannot be collected in the above veins, fingertip blood collection can be performed under certain conditions, such as blood routine, etc. Although the blood collected is peripheral blood, which is somewhat different from venous blood, the error is usually small and can be used for reference.