SearchDiagnosing 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 dilation.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
Tests to confirm the diagnosis of DVT include imaging studies and blood tests, such as:
- Venous ultrasonography
- Venography
- D-dimer measurements
Venous ultrasonography
Venous ultrasonography (also called compression ultrasonography) is the most widely used method for evaluating suspected DVT.25 This safe, noninvasive test involves imaging and compressing the femoral veins down to the most proximal calf veins. DVT is diagnosed when a vein cannot be fully compressed or the test detects an absence of blood flow or a visible thrombus.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. However, in symptomatic patients, a probability score is not an absolute necessity.43 The most commonly used clinical probability score for DVT has been described by Wells and colleagues.45 This tool quantifies the likelihood of an individual patient having DVT based on his or her history, physical examination, and basic laboratory results. Clinical judgment therefore plays a critical role in DVT diagnosis. However, an objective imaging technique must be used to confirm or to rule out DVT in patients with high clinical probability.
Popliteal vein
Venography
Venography is 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, the study 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
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 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 is best used to rule out VTE (ie, if the results are negative, VTE is unlikely). D-dimer tests are even less specific in hospitalised, postoperative, and elderly patients.
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Windows Live- 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. Available at 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.
- 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.
- 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.
- 46 - Saad WE, Saad N. Computer tomography for venous thromboembolic disease. Radiol Clin North Am. 2007;45(3):423-445.
- 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.
- 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.
