JAMA: Single ultrasound may be sufficient to detect blood clot for low-risk patients

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Previous studies suggest that for patients with a suspected blood clot in a deep vein of a leg, withholding anticoagulation therapy after a negative whole-leg compression ultrasound is associated with a low risk of developing a blood clot during the subsequent three months, suggesting that multiple ultrasounds may not be necessary for low-risk patients, according to a report in the Feb. 3 issue of the Journal of the American Medical Association.

Up to 25 percent of distal deep vein thrombosis (DVT) may move into proximal veins, increasing the risk of pulmonary embolism. “Consequently, practice guidelines recommend serial CUS [compression ultrasound] of the proximal veins five to seven days after an initial negative result to safely exclude clinically suspected DVT. Because only 1 percent to 2 percent of repeat CUS tests detect thrombus propagation, many repeat studies are conducted to detect a small number of DVTs,” the authors wrote.

Whole-leg CUS may exclude proximal and distal DVT in a single evaluation and lessen the need for repeat CUS tests. However, concerns exist regarding the safety of using a single whole-leg CUS to exclude DVT following an initially negative result, according to the researchers.

Stacy A. Johnson, MD, of the University of Utah School of Medicine in Salt Lake City, and colleagues conducted a review and meta-analysis of previous studies to examine the risk of venous thromboembolism in patients with suspected lower-extremity DVT following a single negative whole-leg CUS result for whom anticoagulation was withheld. The authors identified seven studies for the analysis, which included 4,731 patients.

The researchers said that venous thromboembolism or suspected venous thromboembolism resulted in death for 34 patients. These mortalities included 32.4 percent of patients with distal DVT, 20.6 percent of patients with proximal DVT, 20.6 percent of patients with nonfatal pulmonary emboli and 26.5 percent of patients, which may have been related to venous thromboembolism. They also noted that use of a model indicated that the combined venous thromboembolism event rate at three months was 0.57 percent.

“In summary, withholding anticoagulation following a single negative whole-leg CUS result was associated with a low risk for venous thromboembolism during three-month follow-up in patients with suspected DVT,” Johnson and colleagues concluded. “Using a single negative whole-leg CUS result as the sole diagnostic modality in patients with high pretest probability of DVT requires further study.”

In an accompanying editorial, Robert A. McNutt, MD, PhD, of Rush University Medical Center in Chicago, and Edward H. Livingston, MD, of the University of Texas Southwestern Medical Center in Dallas, comment on the findings of this study.

“[B]ased on the meta-analysis by Johnson et al,” they wrote, “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 to individual patients. One helpful approach may be for reports of meta-analyses to include, in detail, the inclusion and exclusion criteria for patients enrolled in the original studies,” McNutt and Livingston wrote.

“However, summary statements from meta-analyses should not be used to guide patient care,” the editorialists cautioned. “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.”

McNutt and Livingston concluded that “meta-analysis may have a useful role in synthesizing available evidence, especially, for example, in identifying signals of potential harm that may not be readily apparent in individual studies. However, meta-analyses are most appropriately used to formulate, but not test hypotheses.”