VENOUS DISEASE

7. What noninvasive test is used to diagnose acute DVT?

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Duplex ultrasound has replaced venous occlusion plethysmography as the accepted standard. Colorflow duplex is useful because it helps to identify small veins from the muscle and fascial layers. The ultrasound assessment involves the following steps:

1. Examine the vein for echogenic thrombus.
2. Compress the vein, using pressure on the ultrasound probe, looking for complete collapse. Inability to compress the vein suggests thrombosis. Partial compression suggests partial thrombosis.
3. A Doppler signal from the vein that is phasic with respiration suggests no proximal occlusive thrombus. A signal that is spontaneously present but nonphasic suggests flow around an occlusion via small collateral veins. Absence of a Doppler signal in the vein suggests absence of flow.

8. Can duplex ultrasound be used for surveillance in patients at high risk for DVT?

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Diagnosis of DVT in asymptomatic patients presents a dilemma. The sensitivity of duplex ultrasound is reduced from the reported 95% to < 80% for above-knee detection of DVT in asymptomatic patients. Calf DVT detection is much worse, with sensitivities as low as 20% in many reported series. However, serial contrast venography, although more specific, is not a practical surveillance strategy.

9. Does venous occlusion plethysmography still have a role in the assessment of DVT?

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Yes. Venous occlusion plethysmography or impedance plethysmography (IPG) has high sensitivity and specificity in detecting occlusive thrombi above the knee, particularly for iliofemoral occlusive thrombi (95%). Because IPG provides functional information about deep venous outflow from the legs, it provides diagnosis of nonvisualized caval or iliac thrombosis, diagnosis of recurrent acute proximal thrombosis superimposed on chronic thrombosis, and functional evaluation of residual or chronic outflow obstruction (venous claudication).

10. What noninvasive tests are useful for evaluation of venous incompetence?

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Doppler ultrasound can detect venous reflux in the deep veins of the legs and in the greater and lesser saphenous veins. With experience, the test can be done using a simple Doppler (continuous wave versus pulsed Doppler), but duplex ultrasound is often used to facilitate identification of the vein segments and valves and to position a pulsed Doppler sample reliably. Some laboratories measure the duration of reflux during controlled proximal compression as an indicator of severity of valve incompetence, but unless a valvuloplasty or valve transposition is planned for the identified incompetent valve, such specific measures appear to have little clinical utility.