Compression Ultrasound May Safely Predict Low VTE Risk

A single negative whole-leg compression ultrasound may safely identify which patients with suspected deep vein thrombosis can forego anticoagulation therapy because they are at low risk for venous thromboembolism, according to a meta-analysis.

But the authors of an editorial cautioned against drawing firm clinical conclusions from the meta-analysis.

For patients assessed for possible DVT, practice guidelines currently recommend serial compression ultrasound imaging of the proximal veins after an initial negative result. Such imaging may minimize the risk that distal DVT is present and could propagate into the proximal veins, putting the patient at risk for VTE. However, only 1%-2% of these repeat studies detect thrombus propagation, making many of the studies ultimately unnecessary.

“Because many distal thrombi appear to resolve without use of anticoagulant therapy, it may be argued that detection and treatment of distal DVT is unnecessary because it may place patients at undue risk for anticoagulant-related complications,” wrote Dr. Stacy A. Johnson of the University of Utah, Salt Lake City, and associates (JAMA 2010;303:438-45).

Whole-leg compression ultrasound (CUS) has been proposed as an alternative strategy to improve initial detection of distal DVT and obviate repeat compression ultrasound. But many clinicians are reluctant to rely on a single whole-leg CUS for that purpose, citing concerns about the technical feasibility and safety of such an approach, the investigators noted.

The researchers performed a meta-analysis “to address the safety of withholding anticoagulation after a negative whole-leg CUS by providing estimates of the incidence of symptomatic VTE during the 3 months after a single negative result.” They reviewed 156 studies and limited the meta-analysis to 6 prospective cohort studies and 1 randomized clinical trial. Outcomes for 4,731 patients were included.

The combined end point of confirmed VTE and mortality possibly related to VTE developed in 34 (0.7%) of the patients. There were 11 cases of distal VTE, 7 cases of proximal DVT, and 7 cases of nonfatal pulmonary embolism.

Nine deaths may have been related to VTE, but no necropsies were done to establish the causes of death. All of the deaths occurred in acutely ill hospitalized patients or patients with advanced cancer.

“Overall, the risk for symptomatic VTE was low, with a pooled VTE event rate of 0.57%,” the researchers said. “To our knowledge, these results represent the first reported pooled risk assessment of VTE following a negative lower extremity whole-leg CUS result.”

However, “summary statements from meta-analyses should not be used to guide patient care,” cautioned Robert A. McNutt, M.D., Ph.D., of Rush University Medical Center, Chicago, and Dr. Edward H. Livingston of the University of Texas Southwestern Medical Center, Dallas, in their editorial. “Such conclusions are not helpful when the clinical studies are combined and averaged in a way that reduces the complex world of medical care to overly simple and consequently not clinically useful statistical summaries,” they said (JAMA 2010;303:454-5).

“Generalizing the findings related to a diagnostic test or treatment regimen beyond the specific context from which a study was performed is fraught with danger,” Dr. McNutt and Dr. Livingston noted. “For instance, based on the meta-analysis by Johnson et al., clinicians may infer that not initiating anticoagulation treatment after a negative CUS result in some surgical or ambulatory patients at low risk of having VTE may be appropriate; however, that inference may not be true for hospitalized patients or those with cancer.

“Greater detail about individual patient scenarios is necessary to facilitate better application of the study results.”

Disclosures: Dr. Johnson's associates reported receiving consulting and speaker's fees from AGEN Biomedical, Janssen-Ortho, Boehringer Ingelheim, Sanofi-Aventis, AstraZeneca, Pfizer, and Leo Pharma. The editorialists reported that they had no financial disclosures.