How is it diagnosed?

Superficial thrombophlebitis can be diagnosed by the history and findings of a painful, tender, cord-like swelling below the skin. The surrounding skin may be congested and reddened and may feel hot. The patient may sometimes develop a fever and malaise.

Deep vein thrombosis occurs without any presenting symptoms or physical signs in up to 50% of patients, the first sign of the condition being an embolic event when a detached part of a clot lodges in another organ, usually the lung.

• In some cases DVT may result in oedematous swelling of the leg and the limb may be cyanosed (blue-coloured). In other cases the limb may appear pale.
• Swelling is usually restricted to below the knee in lower leg DVT but can involve the whole leg if the thrombosis occurs in the pelvic veins or veins of the thigh.
• The patient may experience pain in the calf, which may be swollen and tender.
• Flexing the ankle, actively or passively, with the leg held straight may induce or worsen pain in the calf (Homan’s sign).
• Distension of existing varicose veins which does not disappear when the limb is elevated may point to obstruction of the deeper veins.

It can be difficult to differentiate DVT from other types of circulatory impairment of the limb. Muscular strain or contusion may mimic the condition.

In many cases the diagnosis can only be established by investigation such as ultrasonography (Ultrasound Doppler measurement) or plethysmography (measurement of the volume of the limb). In the most difficult cases the use of venography (visualisation of the venous system by injecting radio-opaque dye) may be needed but this investigation causes discomfort for the patient and is usually reserved for more difficult cases.

Computed axial tomography (CAT) or Magnetic Resonance Imaging may help to identify the area of thrombosis in some cases and chest radiography and scanning may be needed to exclude pulmonary embolism. A combination of methods may be needed in difficult cases.

More recently an investigation has become available to measure blood levels of a substance known as D-Dimer. This is a specific degradation product released into the circulation by breakdown of a fibrin clot and at high circulating levels can indicate the presence of DVT or a remote embolus.