Answer :
"The correct answer is that blood is often collected in heparinized capillary tubes rather than plain capillary tubes to prevent clotting of the blood.
When collecting blood samples, it is crucial to prevent the blood from clotting, which can interfere with the accuracy of laboratory tests. Heparin is an anticoagulant that inhibits the blood clotting process. Capillary tubes coated with heparin or filled with heparin solution are used to collect blood samples because they prevent clotting by binding to and neutralizing thrombin, a key enzyme in the clotting cascade. This ensures that the blood remains in a liquid state, allowing for accurate test results. Plain capillary tubes do not contain any anticoagulant and thus do not prevent blood from clotting, which can lead to inaccurate test results or the inability to perform certain tests."
The blood is collected in heparinized capillary tubes to prevent clotting. Heparin is a blood thinner and this anticoagulant is produced naturally by mast cells and basophils. But heparin can not dissolve or break the preformed clots.
