Diagnosing Deep Vein Thrombosis

Diagnosing DVT— signs and symptoms

Deep vein thrombosis (DVT) is often asymptomatic. As a result, the problem can remain undetected until a patient develops a symptomatic pulmonary embolus (PE). This potentially life-threatening event then prompts a search for the source of the embolus.^{25, 43} The frequently asymptomatic nature of DVT is one of the reasons why, in patients at high risk (such as those undergoing major orthopaedic procedures involving the hip or knee), optimal medical care involves thromboprophylaxis.

Clinical symptoms of DVT include swelling, pain, and discolouration of the affected extremity. Physical examination may reveal calf tenderness, unilateral oedema, warmth, skin discolouration, and superficial venous dilatation.^{25, 43} However, many of these signs and symptoms can occur in other conditions and therefore have a low predictive value for diagnosing DVT.⁴²

Conditions such as cellulitis, Baker’s cyst, and haematoma should be considered in the differential diagnosis.²⁵

Diagnosing DVT — tests and imaging studies

Approaches for confirming the diagnosis of DVT include predictive scoring systems, imaging studies and blood tests, such as:

Wells score for probability of DVT
Venous ultrasonography
Venography
Magnetic resonance imaging
Biomarkers
D-dimer measurements

Wells score for probability of DVT

The most commonly used clinical score for evaluating the probability of DVT has been developed by Wells and colleagues. This tool quantifies the likelihood of an individual patient having DVT based on their medical history and physical examination. Clinical judgment therefore plays a critical role in DVT diagnosis, as certain risk factors for DVT can be assessed early in the diagnosis process.⁴⁵ However, an objective imaging technique must be used to confirm or to rule out DVT in patients with high clinical probability.

Predictive scores for DVT developed by Wells and colleagues include the following elements:⁴⁵

Score
Active cancer (treatment ongoing or within previous 6 months or palliative)	1
Paralysis, paresis or recent plaster immobilisation of lower extremities	1
Recently bedridden for more than 3 days or major surgery within 4 weeks	1
Localised tenderness along distribution of the deep vein system	1
Entire leg swollen	1
Calf swelling by more than 3 cm when compared with asymptomatic leg	1
Pitting oedema	1
Collateral superficial veins	1
Alternative diagnosis as likely or greater than that of DVT	-2

A high score is 3 or more, a moderate score 1 or 2 and a low score 0 or less.⁴⁵

Venous ultrasonography

Venous ultrasonography (also called compression ultrasonography or ultrasound) is the most widely used method for evaluating suspected DVT.²⁵ This safe, non-invasive test involves compressing and imaging the femoral veins down to the most proximal calf veins.⁴⁴ Despite some limitations (eg, operator dependence, lack of sensitivity in patients with oedema or significant obesity, inability to distinguish between an old clot and a fresh thrombus), ultrasonography is considered acceptable when combined with a probability score based on clinical variables.⁴³

Popliteal vein

Venography

Venography had been considered the gold standard for diagnosis.^{42, 43} This test detects both calf DVT and more proximal thrombi. However, venography has the drawbacks of being invasive, painful, and expensive. For this reason, this diagnostic test is usually reserved for situations when clinical suspicion of DVT is not supported by ultrasonography findings. A related diagnostic test option, the indirect CT venogram, can be done at the same time as CT pulmonary angiography, with sensitivity and specificity comparable to ultrasound.⁴⁶

Magnetic resonance imaging

Magnetic resonance imaging (MRI) employs a powerful magnetic field to generate a high-resolution image of anatomic structures. This non-invasive study may be used to diagnose DVT in patients when ultrasound examination is inappropriate or not feasible.^{216, 258} Unlike CT venography, MRI does not involve radiation exposure.

D-dimer measurements

D-dimer is a protein fragment produced by clot degradation. It is formed when plasmin dissolves the fibrin strands that hold a blood clot together.^{43, 199} D-dimer blood tests vary in their accuracy. None is specific, but some have high sensitivity. For this reason, a highly sensitive D-dimer test has high negative predictive value (ie, if the results are negative, VTE is unlikely).¹⁹⁹ D-dimer tests are even less specific in hospitalised, postoperative, and elderly patients.

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Article references

25 - Turpie AG, Chin BS, Lip GY. Venous thromboembolism: pathophysiology, clinical features, and prevention. BMJ. 2002;325(7369):887-890.
43 - Kearon C, Hirsh J. Cardiovascular medicine: XVIII. Venous thromboembolism. In: Dale DC, ed. ACP Medicine. New York, NY: WebMD, Inc; 2007:1-15. http://www.acpmedicine.com/acp_home.htm. Accessed February 12, 2008.
42 - Ramzi DW, Leeper KV. DVT and pulmonary embolism: Part I. Diagnosis. Am Fam Physician. 2004;69(12):2829-2836.
45 - Wells PS, Anderson DR, Bormanis J, et al. Value of assessment of pretest probability of deep-vein thrombosis in clinical management. Lancet. 1997;350(9094):1795-1798.
44 - Stern JB, Abehsera M, Grenet D, et al. Detection of pelvic vein thrombosis by magnetic resonance angiography in patients with acute pulmonary embolism and normal lower limb compression ultrasonography. Chest. 2002;122(1):115-121.
46 - Saad WE, Saad N. Computer tomography for venous thromboembolic disease. Radiol Clin North Am. 2007;45(3):423-445.
216 - Kluge A, Mueller C, Strunk J, Lange U, Bachmann G. Experience in 207 combined MRI examinations for acute pulmonary embolism and deep vein thrombosis. AJR Am J Roentgenol. 2006;186(6):1686-1696.
258 - Sampson FC, Goodacre SW, Thomas SM, van Beek EJ. The accuracy of MRI in diagnosis of suspected deep vein thrombosis: systematic review and meta-analysis. Eur Radiol. 2007;17(1):175-181.
199 - Goldhaber SZ. Cardiovascular medicine: XVIII. Venous thromboembolism. In: Dale DC, ed. ACP Medicine. New York, NY: WebMD, Inc; 2010:1-15.

Thromboprophylaxis: The use of medication or medical devices to prevent the formation of blood clots.
Oedema: The presence of abnormally large amounts of fluid in the intercellular tissue spaces of the body, usually used to describe demonstrable accumulation of excessive fluid in subcutaneous tissues.
Compression ultrasonography: Ultrasonography scanning is widely used in medicine as an effective method of imaging the soft tissues of the body. Compression ultrasonography combines real-time imaging of the deep veins with venous compression to diagnose DVT. It has become the noninvasive method of choice for DVT diagnosis on the basis of its excellent accuracy and wide availability.
Angiography: Angiography is imaging of the blood vessels using X-rays or magnetic resonance tomography. The vessels are visualised by injecting contrast medium into a vein. Angiography is used to diagnose disorders of the blood vessels.
Venography: An X-ray of the veins performed by first injecting a radiopaque contrast (shows up on X-ray) into the vein in question and then taking a conventional X-ray. Used to demonstrate blockage of a vein. Commonly used in the lower extremities to diagnose DVT.
Computed tomography: Also know as CAT scan. A radiographic technique that uses a computer to assimilate multiple X-ray images into a two-dimensional cross-sectional image.
Fibrin: The primary end product of the coagulation cascade. Fibrin links itself into strands to form a net. This net traps blood cells and tightens itself through cross-linkages, resulting in a dense blood clot.
Plasmin: A component (enzyme) of the fibrinolytic system that breaks fibrin into small pieces.
Venous thromboembolism: A condition in which a blood clot (thrombus) forms in a vein, which in some cases then breaks free and enters the circulation as an embolus, finally lodging in and completely obstructing a blood vessel, e.g., in lungs causing a PE. The term encompasses both DVT and PE.