161 consecutively admitted medical patients with the clinical suspicion of acute deep venous thrombosis (DVT) were thermographed and phlebographed in order to study the congruence of these methods. The sensitivity of thermography in the detection of DVT was found to be 99%, whereas the specificity was only 49%.
The low specificity is explained by the fact that all thermographs suggestive of DVT were classified as pathologic to keep the sensitivity of the method as high as possible. Patients with dilated veins which may closely resemble DVT on thermography may in these cases give false positive results.
Of 76 patients with phlebographically verified DVT, 22% became thermographically normal within 22 days, whereas 78% did not normalize within the mean observation time of 31 days.
In another part of the study all medical patients (101) who were residing in our wards during a period of a week were screened by means of thermography. From this unselected group 17 patients were found to have thermographs suggestive of DVT. In 5 of these patients no reason for pathological thermography could be found.
Thermography is a cheap and highly sensitive screening method for DVT, but findings of false positives caused by older thromboses and dilated veins are not unusual. The frequency of such false positives may be minimized by performing thermography after exercise.