Pitfalls of the Doppler examination for venous thrombosis.

In a prospective study comparing Doppler ultrasound and contrast venography in 112 patients, we identified all false-negative and false-positive results obtained by Doppler and are reporting those errors that we believe are commonly occurring pitfalls of this technique. There were 21 false-negative and nine false-positive examinations. False-negative examinations were caused by the following factors: thrombi isolated to the veins of the calf (13 patients); nonocclusive clot involving or proximal to the popliteal vein (3); incorrect interpretation of examinations done by inexperienced personnel (2); acute thrombosis masked by changes of severe chronic disease (1); misinterpretation of increased saphenous flow in the presence of an occluded superficial femoral vein (1); and bilateral clot with one leg having significantly more evidence of venous obstruction than the other (1). Factors in the nine false-positive examinations were chronic disease interpreted as acute thrombosis (3), interpretation of weak signals in the calf as thrombosis (3), weak signals due to obesity (2), and excess Doppler probe pressure distorting venous flow (1). We conclude that results of the Doppler examination should be questioned when there is a suspicion of thrombus in the deep veins of the calf, the question of a nonocclusive thrombus, or the presence of chronic venous changes related to previous deep venous thrombosis.