By what coagulation pathway does clotting occur in blood sample collected in a capillary tube?

The extrinsic pathway begins with the release of tissue thromboplastin(tissue factor ) in response to vascular injury or contact between traumatized extravascular tissue and blood. Since there is no source of tissue thromboplastin release as the blood is with the capillary tube, thus clotting proceeds intrinsic pathway only (i.e. activation of factor XII). the intrinsic pathway requires exposure of factor XII (HAGEMAN FACTOR) to a negatively charged surface such as glass capillary tube.