 Compression ultrasonography has both high sensitivity and specificity for detecting proximal DVT but only in symptomatic patients . Results are not reliable when the patient is <unk> and must be checked carefully . For example , in high risk post @-@ operative patients , mainly after orthopedic surgery where there is already lower limb pain and edema following surgery , <unk> can be localized in the calf veins and often these are not completely occlusive . 
