Impedance plethysmography: its limitations as a substitute for phlebography.

Impedance plethysmography (IPG) was used to study 132 legs: 100 in normal volunteers not subjected to radiocontrast phlebography, seven in patients whose limbs were phlebographically normal, and 25 proven by phlebography to have deep venous thrombosis (DVT). There were no false positive IPG results when a maximum venous outflow of 0.2% was the discriminant. However, in the 25 legs with thrombosis in calf, popliteal, femoral, and iliac veins, clots were not detected by IPG in 44--51% of legs, depending upon the discriminant. These results, which are in agreement with data reported elsewhere, indicate that it is reasonable to use the IPG method as the sole diagnostic maneuver when the test result is clearly abnormal, but that if the result is not abnormal, a radiocontrast phlebogram is necessary.