How Do Capillary Tubes Collect Blood?

How Do Capillary Tubes Collect Blood? The capillary tube uses capillary action to draw the blood into the micro tube thereby eliminating the tendency for scooping. Because the capillary tube is also coated with anticoagulant, the blood sample mixes with it immediately to prevent clotting. How is capillary puncture done? The puncture must be on