After tooth extraction to determine the existence of blood clots can be based on symptoms or observation. 1. Symptoms: after tooth extraction, generally cotton ball pressure wound for about half an hour, filled with blood in the alveolar fossa to form a blood clot, to achieve the role of wound hemostasis, spit out the cotton ball will have a small amount of blood seepage, which is a normal phenomenon, if there is a lot of bleeding, it means that the blood clot falls off and fails to achieve the role of hemostasis, you can once again bite the cotton ball for 30-60 minutes to stop the bleeding. 2. Observation: you can open your mouth and observe the wound, and find that the wound is empty and accompanied by severe pain or a large amount of blood outflow, which means that the blood clot has been dislodged, and needs to be reviewed and dealt with. If you find any abnormality in the wound after tooth extraction, you should go for follow-up examination and treatment under the guidance of the doctor to avoid delaying the condition.