Two-point ultrasonography equivalent to whole-leg for DVT diagnosis

Serial two-point ultrasonography of the proximal veins was found to be as effective as the more complex whole-leg ultrasonographic method in diagnosing deep vein thrombosis of the lower extremity.

Ultrasonography of the entire deep vein system was previously considered a better option than two-point ultrasonography due to its ability to detect isolated calf DVT, but randomized comparisons had not been conducted. Whole-leg ultrasonography requires skilled operators and thus is often not an available option outside of regular working hours.

Researchers at 14 Italian hospitals enrolled 2,098 patients with suspected DVT of the lower extremity. Patients were randomly assigned to either two-point plus D-dimer testing (n=1,045) and whole-leg ultrasonography (n=1,053). Of these, 801 patients in the two-point ultrasonography group and 763 patients in the whole-leg group had normal findings and were followed for three months.

Symptomatic venous thromboembolism occurred in seven of the 801 patients in the two-point group, for an incidence of 0.9% (95% CI, 0.3-1.8). In the whole-leg group, nine of the 763 patients had a VTE for an incidence of 1.2% (95% CI, 0.5-2.2). This observed difference of 0.3% (95% CI -1.4-0.8%) met the criteria for equivalence of the two tests.

“The results of the trial … show that whole-leg ultrasonography has little advantage, unless a course of anticoagulant therapy for isolated calf DVT is preferable to repeating two-point ultrasonography a week later,” wrote C. Seth Landefeld, MD, of the University of California in San Francisco, in an accompanying editorial. He added that the available evidence now suggests that the first step in assessing possible DVT is with either a clinical prediction rule and a D-dimer test, a clinical prediction rule and two-point ultrasonography or a two-point ultrasonography along with a D-dimer test.

JAMA. 2008;300:1653-1659.

This is another example of the devilish details that are often missing from 'evidence-based-medicine' derived recommendations. I recently opined in a medical malpractice case of a fatal pulmonary embolism following a missed calf clot. The patient, a middle-aged, obese woman on estrogen-replacement therapy, developed increasing pain above her ankle fracture that had been surgically repaired two weeks before. D-dimer was not assayed, but probably would have been positive (DVT or not) due to recent trauma so would not have been useful. 'Clinical criteria' as traditionally formulated and used by those impressed with 'cookbook medicine' provided an overly optimistic negative prediction, since these criteria do not include important DVT risk factors such as obesity, estrogen usage nor positive family histories — all red flags in this case. Finally, whole leg ultrasound is 30% insensitive in detecting calf clots in most institutions and missed the fatal, propagating one in this case. High-risk, high-suspicion patients should have repeat ultrasonography two to three days after negative studies (or even better have venography).

– Harry S. Jacob, MD

HemOnc Today Chief Medical Editor