Ultrasonography in the evaluation of low-extremity deep vein thrombosis

Deep vein thrombosis (DVT) is a common disorder that may be difficult to diagnose clinically (accuracy: 58%e70%) but carries significant morbility and mortality if unrecognized or untreated. Because there is a high incidence of lower-extremity DVT (70%e75%) in patients with arteriographically documented pulmonary emboli (PE), early detection of DVT is of significant value to decrease the risk of life-threatening PE. Clinical diagnosis of lower-extremityDVTrequires confirmation by imaging study before committing the patient to anticoagulation therapy. Ultrasonography (US) is currently the principal imaging technique used for the detection of venous thrombosis in the extremities. Studies have shown that demonstrating compressibility of leg veins under US is accurate for ruling out DVTwhen performed by vascular imaging specialists. Some other methods have been used for the detection or diagnosis of DVT, including plethysmography, Tc-labeled fibrinogen scintigraphy, D-dimer assay, and contrast venography. Contrast venography, once the diagnostic test of choice for lowerextremity DVT, has been considered the gold standard; but because it is invasive, expensive, or may be technically incomplete or uninterpretable, and can occasionally induce venous thrombosis, it is not an optimal screening technique for detecting DVT and has been largely replaced by lower-extremity duplex US in recent years. US, with its noninvasive nature, high availability, ease of performance, and high accuracy in diagnosis, has been chosen as the initial study in the evaluation of suspected DVT in the last two decades. This noninvasive diagnostic method approaches contrast venography in accuracy for diagnosis of proximal lower-extremityDVT.However, it falterswhen calf venous thrombosis is present, showing a sensitivity of approximately 40%e70%. Standard lower-extremity duplex US guidelines have included repeat examinations at Day 1 and 3e7 days after a normal study. This protocol was initiated to catch the 20% of calf thrombi that will propagate proximally. Some recent studies have indicated that one repeat examination at 5e7 days after an initial negative result may be necessary to ensure a more accurate diagnosis. Although lower-extremity duplexUShas become thepreferred test for diagnosing DVTs, it is not always available around the clock. Many emergency departments have no access to vascular studies during off hours and are forced to admit even relatively low-risk patients suspected of having lower-extremity DVTs.