A prothrombin time of 21.7 seconds in an eight year old child is abnormal and may be associated with abnormal fibrinogenemia, the presence of heparin in the blood, and other conditions that require treatment. The prothrombin time (TT) is a measure of the time it takes for plasma to show up with fibrin and its multimers, which is 16 to 18 seconds in normal people (TT), and more than 3 seconds over the normal value is abnormal. A prothrombin time of 21.7 is abnormal and may be the result of a disease, which, if not intervened in time, may lead to abnormal bleeding and other damages, which are more serious. Common causes of abnormal prothrombin time (TT) include hypofibrinogenemia, fibrinogen anomalies, increased heparin-like substances in heparin therapy states, systemic lupus erythematosus, and liver disease. Hypofibrinogenemia and fibrinogen abnormalities can be treated with fibrinogen infusion and plasma transfusion; prolonged TT during heparin therapy is a normal drug reaction; and increased heparin-like substances require treatment of the primary disease. It is recommended to go to the hospital in time to see a specialist who will evaluate the condition and intervene according to the cause of the disease.