Deep vein thrombosis of the lower extremities auxiliary examination is as follows: 1. Laboratory examination: At present, most primary hospitals can carry out D-dimer examination, if the D-dimer examination is elevated, it does not necessarily mean that there is thrombosis. Except for the cases of recent major surgery, trauma, myocardial infarction and gastrointestinal bleeding, elevated D-dimer without obvious reasons should be highly suspected of having deep vein thrombosis. If D-dimer is normal, deep vein thrombosis can be basically excluded; 2.Lower extremity vascular ultrasound: a simple lower extremity vascular ultrasound can clarify the presence of thrombosis in the veins; 3.CTV: that is, CT venous imaging, including nuclear magnetic venous imaging, but the primary hospital examination may not be carried out; 4.Lower extremity venography: the gold standard of vascular surgery, because lower extremity venography is an invasive test, will not be preferred This kind of examination. Therefore, in many hospitals, including the primary hospitals, the thrombosis is mainly examined by lower extremity vascular ultrasound. At present, the most routine examination is D-dimer and color ultrasound, which can basically clarify the lower extremity venous thrombosis.