 It is clinically important to determine the location and extent of DVT [3,6]. DVT that is limited to the infrapopliteal calf veins (ie, below-the-knee or distal DVT) often resolves spontaneously and is rarely associated with pulmonary embolism or other adverse outcomes [3,7,8]. Above-the-knee or proximal DVT, on the other hand, is strongly associated with an increased risk for pulmonary embolism. The treatment of choice for DVT is anticoagulation to reduce the risk of DVT extension, recurrent DVT, pulmonary embolism, and post-thrombotic syndrome. It is generally accepted that the benefits of anticoagulation therapy in patients with proximal DVT outweigh its risks [3,6]. Because below-the-knee DVT rarely results in pulmonary embolism, the role of anticoagulation therapy in patients with distal DVT remains controversial [3,6,9]. However, because one-sixth of patients with distal DVT experience extension of thrombus proximally above the knee, serial imaging to exclude proximal DVT extension is recommended at 1 week if anticoagulation therapy is not initiated at presentation [3,6]. This issue is complicated by the variability in evaluation for below-the-knee DVT as part of a routine examination. Classically, a patient with symptomatic lower extremity DVT presents with either local pain or tenderness or with edema and swelling of the lower extremity. However, approximately one-third of patients with DVT do not have any symptoms [10]. Often, symptoms are not apparent until there is involvement above the knee [3]. The clinical diagnosis of DVT using clinical risk-stratification scores (eg, Wells score) alone has, therefore, been less than ideal [10]. Wells et al [11,12] suggested using a clinical DVT-prediction score (aka, Wells score) in combination with a blood evaluation for plasma D-dimer, a degradation product of cross-linked fibrin that is elevated during thromboembolic events.
Suspected Lower Extremity Deep Vein Thrombosis.  It is clinically important to determine the location and extent of DVT [3,6]. DVT that is limited to the infrapopliteal calf veins (ie, below-the-knee or distal DVT) often resolves spontaneously and is rarely associated with pulmonary embolism or other adverse outcomes [3,7,8]. Above-the-knee or proximal DVT, on the other hand, is strongly associated with an increased risk for pulmonary embolism. The treatment of choice for DVT is anticoagulation to reduce the risk of DVT extension, recurrent DVT, pulmonary embolism, and post-thrombotic syndrome. It is generally accepted that the benefits of anticoagulation therapy in patients with proximal DVT outweigh its risks [3,6]. Because below-the-knee DVT rarely results in pulmonary embolism, the role of anticoagulation therapy in patients with distal DVT remains controversial [3,6,9]. However, because one-sixth of patients with distal DVT experience extension of thrombus proximally above the knee, serial imaging to exclude proximal DVT extension is recommended at 1 week if anticoagulation therapy is not initiated at presentation [3,6]. This issue is complicated by the variability in evaluation for below-the-knee DVT as part of a routine examination. Classically, a patient with symptomatic lower extremity DVT presents with either local pain or tenderness or with edema and swelling of the lower extremity. However, approximately one-third of patients with DVT do not have any symptoms [10]. Often, symptoms are not apparent until there is involvement above the knee [3]. The clinical diagnosis of DVT using clinical risk-stratification scores (eg, Wells score) alone has, therefore, been less than ideal [10]. Wells et al [11,12] suggested using a clinical DVT-prediction score (aka, Wells score) in combination with a blood evaluation for plasma D-dimer, a degradation product of cross-linked fibrin that is elevated during thromboembolic events.