Rationale.

THE QUESTION: IS THERE A DEEP VEIN THROMBOSIS?

Deep vein thrombosis (DVT) is a common problem worldwide, affecting ≈1 per 1000 adults annually (4). Around one-third of patients presenting with a symptomatic DVT will later manifest a pulmonary embolism (PE), while 90% of all PEs originate from a DVT. In the UK, PE is responsible for killing approximately 8000 people per annum, and, in reality, the incidence of both PE and DVT is probably much higher due to significant under-diagnosis (1). As a result, it is essential to implement effective tools for early and accurate diagnosis of DVT; also ensuring a timely treatment.

WHY USE ULTRASOUND?

Although a painful or swollen leg is a frequent complaint in the ED, a textbook clinical presentation of DVT accounts for no more than 20% of cases and remains non-specific. Hence, clinical examination alone is unreliable, and further investigation is often required. A radiologist-performed ultrasound (US) is the first-line diagnostic test for detecting lower limb deep-vein thrombosis. However, as this requires coordination with a different service, patient transfer, and waiting for the report, it is time-consuming and impractical in the ED setting. Additionally, is often only available in-hours or not available at all.

In this context, the whole-leg standard US has been simplified into a two-point compression US that is easy to learn and rapid to perform, decreasing the demand on the Radiology Department and optimizing costs and patient flow in the ED. More importantly, when paired with D-dimer and validated prediction score, namely the wells score, it provides a reliable diagnostic tool at the point of care (5). Moreover, the accuracy of emergency physician-performed ultrasound for the diagnosis of DVT has proven to be high and comparable to the reference standard, showing both sensitivity and specificity superior to 96% (6).

LIMITATIONS

The now classic two-point DVT assessment is a narrowed-down exploration of the common femoral and popliteal veins, as such its main limitation is missing DVT in other locations. More recent evidence involving a large cohort of patients with confirmed DVT showed that 6.3% of them had thrombi in proximal veins other than the common femoral and popliteal (7). These results support the idea that sonographic assessment for DVT in the ED should also include the superficial and deep femoral veins. Also, as calf veins assessment is not part of the routine examination, another limitation of two-point compression US is missing isolated below-knee DVT. As such, some authors even propose the sonographic exploration of the whole extremity in the ED (2).

Alternatively, it should also be considered that patients with previous venous disease, including DVT, may have incompressible veins, resulting in a false-positive result.

Lastly, bear in mind that compression ultrasound does not rule out DVT on its own and works as an adjunct to clinical reasoning, prediction tools, and D-dimer. Hence, the decision-making process should always be a combined strategy.

In DVT the major health risks are propagation and/or embolization. The risk of embolization in a patient who may have below-knee DVT, but with no evidence of proximal DVT on compression US, is quoted as between 0.7% and 1.1%. However, the risk of propagation of below-knee DVT is quoted as ranging from 2% to 36%. Therefore, patients who have normal three-point compression testing, but who are at high risk for DVT as defined by a validated clinical assessment tool, should have a repeat scan at approximately 1 week. Local treatment protocols should be followed as regards indication for anticoagulation during this period (1).