Our vascular laboratory provided diagnostic data for the RD Heparin study and we have concerns about the design of Davidson and colleagues' study [1] comparing color Doppler ultrasound to contrast venography for the diagnosis of deep venous thrombosis (DVT).

The data were collected from only 7 of the 20 centers in the RD Heparin study. They were retrospectively selected on the basis of a questionnaire, in which each center declared whether they used color Doppler ultrasound for the diagnosis of DVT. In our laboratory, all study patients were examined with color Doppler ultrasound equipment, but our data were arbitrarily excluded because we do not use the color image as a criterion for diagnosis of DVT. We rely primarily on confluent examination of venous segments with real-time B-mode imaging and compression maneuvers.

The authors submitted data from our laboratory for another study [2]. In this study, duplex scanning had a sensitivity of 100% in detecting four cases of proximal DVT and had an overall accuracy of 86% for evaluation of calf or thigh veins when compared with venography. However, if duplex scanning had been declared the gold standard, venography would have had an accuracy of only 87% because it missed six cases of DVT of the calf and one of DVT of the thigh. These results are much better than those reported in the Annals article and would not support the conclusion by Davidson and colleagues that duplex scanning is insensitive and "should not be substituted for venography".

Any multicenter study using ultrasound should be designed to ensure that examinations are done in a consistent fashion with comparable equipment; this was not done in the current study. In addition, it is well known that patients with perioperative hip and knee arthroplasty are among the most technically difficult patient groups to examine by duplex scanning, further contributing to the poor results reported for color Doppler ultrasound.

The above concerns notwithstanding, we actually agree with the conclusion that color Doppler imaging is an inferior method for diagnosing DVT. Unfortunately, most Annals readers do not have adequate background knowledge to realize that properly performed duplex scanning remains the test of choice for diagnosis of DVT in most patients. Color Doppler is useful for anatomic orientation and for enhancing the speed of examination but it should not be relied on to provide the diagnosis of DVT.