Invasive and noninvasive techniques in the detection and evaluation of acute venous thrombosis.

There are a variety of noninvasive testing procedures which can be used to establish the diagnosis of acute venous thrombosis with a high degree of certainty. For prospective screening of patients at risk, only 125I-labelled fibrinogen is of value, but does have a false positive rate of 21%. Its greatest problem is that it must be given prior to the event and, furthermore, it is not accurate in the upper thigh or the region of the iliac veins. Doppler ultrasound, plethysmography and phleborheography are accurate methods of detecting thrombi which involve the major veins of the limb from the level of the tibial veins below the knee to the level of the iliac veins in the abdomen. If properly performed, the sensitivity and specificity should exceed 90% in experienced laboratories. Contrast phlebography remains the best method of demonstrating venous thrombosis but does have limitations with regard to costs, pain to the patient and the production of thrombosis in a small percentage of patients. Furthermore, if the injections are done at the foot level, at least 18% will have inadequate visualization of the iliac veins, a critically important venous segment. It use must be restricted to those situations in which the noninvasive tests are equivocal or the information is absolutely essential for a therapeutic decision.