Impedance Testing for Venous Thrombosis

Deep vein thrombosis is a common postoperative complication whose clinical diagnosis is notoriously unreliable. A fatal pulmonary embolism may be the first clinical indication of extensive clots in the leg veins. Understandably, any new diagnostic test for venous thrombosis arouses a great deal of interest.

One promising method for the diagnosis of deep thrombophlebitis is based on electrical impedance measurements, which provide a convenient indirect means for quantitating changes in venous blood volume. The method has great appeal because it can be carried out at the bedside and is safe and simple for the patient. However, the diagnostic accuracy in different hospitals has varied. Although some authors have found impedance testing quite reliable,^1,2 one group of investigators has reported a high incidence of false positive results.^3,4 Still another group has found no false positive tests, but has reported several false negative results.⁵ Elsewhere in this issue Gazzaniga