DVT may develop in the lower or upper extremities. Although up to 18% are located in the upper extremities,⁵ the majority arise from the lower extremities. In the lower extremities, DVT is referred to as proximal when it is found in the popliteal veins or higher and as distal when it is located in the calf.

Perspective

Unfortunately, the diagnosis of DVT cannot be made on clinical signs and symptoms alone. The location of swelling and pain does not correlate with the location or extent of the clot, and symptoms localized to the calf may have an etiology in more proximal veins.⁶ Clinical signs have been analyzed statistically and found to be of little value in reliably determining the presence or absence of DVT.⁷ The differential diagnosis for leg pain and swelling includes lymphedema, chronic venous insufficiency, infection (cellulitis), aneurysm, pseudoaneurysm, Baker cyst, and other musculoskeletal causes. Diagnosis of DVT depends on the clinician’s pretest probability assessment and a combination of several noninvasive diagnostic tools (lower extremity ultrasound, D-dimer, or both). The exact diagnostic path or algorithm pursued depends somewhat on local availability and expertise. When available, lower extremity ultrasound is the primary modality used to diagnose or exclude DVT. The lower extremity ultrasound may be a proximal lower extremity examination, a whole-leg examination, or an abbreviated, two-point compression examination. If proximal lower extremity ultrasound is performed, current practice guidelines recommend that ultrasound of the proximal veins be repeated 5 to 7 days after an initial negative result to safely exclude clinically suspected DVT.^8,⁹ This recommendation stems from the observation that up to 20% of cases of distal DVT may propagate into the proximal veins.^10,¹¹ A systematic review and metaanalysis published in 2010 found that after a negative whole-leg study, anticoagulation may be withheld safely without the need for a repeated ultrasound examination.¹²

Despite the numerous benefits of lower extremity sonography, many emergency providers continue to be unable to obtain lower extremity ultrasound after hours, on weekends, and on holidays. Clinician-performed two-point compression lower extremity ultrasound is now considered an appropriate method for assessing lower extremity DVT in the emergency department (ED) and is one of the 11 core emergency ultrasound applications.^13,¹⁴ Emergency providers who perform two-point compression lower extremity sonography have demonstrated scan times of less than 4 minutes per patient and time savings of more than 2 hours in terms of time to patient disposition.^15,¹⁶ When ultrasound is not available, providers may be forced to administer low-molecular-weight heparin and either keep the patient in the ED overnight or coordinate an outpatient study for the patient the following day. Although the risk for bleeding in these situations is low, boarding the patient in the ED or relying on patient-initiated follow-up is less than ideal. Given ever-increasing patient volumes and ED crowding, the value of clinician-performed two-point compression lower extremity ultrasound cannot be overstated.

Evidence-Based Review

Radiology-performed lower extremity duplex ultrasound has reported sensitivities of 91% to 96% and specificities of 98% to 100%.^17,¹⁸ Multiple studies have demonstrated that clinician-performed two-point compression bedside ultrasound can be accurate in detecting DVT when compared with radiology-performed examinations.¹⁹^–²² In a systematic review, Burnside et al. found an overall sensitivity of 95% and specificity of 96% for detection of lower extremity DVT by emergency physician–performed ultrasound.¹⁹ The authors caution that the six studies included in their analysis were limited by small sample size and by emergency physicians with high levels of ultrasonographic expertise, thus leaving their estimates at risk for being overly optimistic. A prospective study by Kline et al. in the same year assessed a more diverse range of clinician sonographers with more limited training in ultrasonography and found a sensitivity of 70% and specificity of 89%.²⁰ They concluded that ultrasound performed by providers with limited training in compression ultrasonography of the lower extremity had intermediate diagnostic accuracy that may be improved by pretest probability assessment. A more recent prospective study by Crisp et al. included a large, heterogeneous group of emergency providers with variable levels of ultrasonographic experience but found the test results to be similar to those from the Burnside review with a sensitivity of 100% and specificity of 99%.²¹

It is important to note that clinician-performed lower extremity sonography focuses on compressibility and typically does not include color flow Doppler or pulsed wave spectral Doppler beyond its use to localize or distinguish between vessels. Compressibility of veins with gray-scale B-mode ultrasound is the most important criterion and is widely accepted as being highly accurate.⁷ Color flow Doppler and pulsed wave spectral Doppler provide additional information and may be particularly useful when uncertainty exists or when assessing for pelvic DVT. Even though Doppler imaging has utility, it can be limited by the following: nonocclusive thrombus, the presence of collateral flow, and sonographer skill. Some studies have found that Doppler adds little to the information obtained by compression ultrasound for the detection of proximal DVT.²² In a prospective study by Biondetti et al., vein compressibility alone was compared with contrast-enhanced venography and found to have an overall sensitivity of 87% and a specificity of 100%.²³ Because six of the seven false-negative examinations resulted from isolated distal DVT, the sensitivity of compression-only ultrasound for detecting proximal DVT was noted to be 98%. It is reasonable that clinician-performed lower extremity ultrasound studies consist only of compression.

Two-Point Compression Versus Whole-Leg Color Duplex Ultrasound

Two-point compression lower extremity ultrasound is a simplified approach that consists of compression of the common femoral vessels in the groin and the popliteal vessels in the popliteal fossa. The concept behind this abbreviated approach stems from the idea that clot usually involves multiple or whole venous segments. Several studies have shown that few cases of proximal DVT occur without involving either the common femoral vein (CFV) or the popliteal vein (PV), or both, and that isolated thrombus in the superficial femoral vein (SFV) is rare.²⁴^–²⁷ In a study of limited compression ultrasound in patients with symptomatic DVT, Pezzullo et al. found a 54% reduction in examination time (9.7 minutes) while still maintaining high accuracy and patient safety.²⁶ To the contrary, Frederick et al. prospectively studied 721 symptomatic patients and determined after 755 examinations that DVT limited to a single vein occurs with sufficient frequency that the lower extremity ultrasound cannot be abbreviated without resultant loss of diagnostic accuracy.²⁸ To that end, in a retrospective study of 2704 lower extremity ultrasound examinations, Maki et al. found that acute DVT was isolated to the SFV in 22.3% of patients with DVT.²⁹ They concluded that abbreviated imaging studies that evaluate only the CFV and PV could fail to detect up to 20% of proximal DVT and recommended interrogation of the SFV. The question of whether two-point compression can be performed in place of full-length examination remains controversial. In clinical situations in which radiology-performed, whole-leg sonography is not available, there is little controversy; clinicians should proceed with performing two-point compression lower extremity ultrasound. One solution to the vexing problem of missed SFV clots is to perform “two-region” compression ultrasound—that is, perform compression in the groin region from the greater saphenous junction through the bifurcation of the superficial and deep femoral veins and perform compression in the popliteal region from the PV to the trifurcation of the distal calf veins. This “two-region” approach has not been studied as a specific technique, although previous research would seem to support it as a compromise approach.

The value of whole-leg color duplex ultrasound is dependent on the significance of identifying distal DVT. The clinical relevance plus need to treat distal DVT is a controversial topic that continues to be debated. Proponents of full-length lower extremity examination point to a randomized trial by Lagerstedt et al. in which the usefulness of long-term anticoagulation (for 3 months) was assessed in patients with distal DVT. The authors found that those who did not receive long-term anticoagulation therapy had a significantly higher recurrence rate than those who did (8 of 28 patients versus 0 of 23 patients; P < .01).³⁰ This study suggests that calf vein thrombi are important, should be sought in symptomatic patients, and when found, should be treated with long-term anticoagulation. Although the American College of Chest Physicians is in agreement with these findings,³¹ there is no universally accepted consensus on the management of distal DVT.³² Proponents of full-length examination often point to literature in which a proximal progression rate of up to 20% has been observed.^10,¹¹ Righini et al. contend that there is considerable uncertainty over the natural history of distal DVT and, in particular, over the rate of extension to proximal veins.³³ The authors argue that if identifying and treating distal DVT do not improve patient outcomes, whole-leg color duplex ultrasound is of less clinical utility. Previous trials have demonstrated that it is safe to withhold anticoagulation in patients with suspected venous thrombosis and negative serial proximal ultrasound results even though some patients have calf vein thrombi.³⁴ In a more recent, prospective, randomized multicenter study, Bernardi et al. compared serial two-point ultrasonography plus D-dimer testing with whole-leg color-coded Doppler ultrasonography for diagnosing suspected symptomatic DVT.³⁵