CT scan after unprovoked blood clot is too much medicine

The diagnosis and and treatment of patients with deep venous thrombosis and pulmonary embolism is a common task in family medicine. In many instances, venous thromboembolism (VTE) is "provoked" by one or more predisposing risk factors, such as prolonged immobility, major surgery, pregnancy, or thrombophilia. In patients with a first episode of VTE without any known risk factors, one question that arises is how aggressively to test for a possible occult cancer, which may be present in up to 10 percent of cases. A Cochrane review of two small studies found inconclusive evidence that extensive testing for cancer improved cancer-related mortality compared to limited testing, although one study suggested that extensive testing advanced the time of cancer diagnosis.

A multicenter, randomized, controlled trial of 854 adults (mean age 54 years) with unprovoked VTE published in the New England Journal of Medicine provided more evidence to guide clinical decision-making. The control group underwent basic blood testing, chest radiography, and screening for breast, cervical, and prostate cancer; the intervention group received these tests and a computed tomography (CT) scan of the abdomen and pelvis. (25 percent of both groups had already received CT pulmonary angiography to diagnose a pulmonary embolism.) The primary outcome was confirmed cancers detected after one year of follow-up that were not diagnosed by the initial screening strategy. The trial found no statistical differences between the two groups in the primary outcome (missed cancers), mean time to a cancer diagnosis, or cancer-related mortality.

Since a CT of the abdomen and pelvis exposes a patient to a considerable dose of radiation and greatly increases the risk of detecting an incidentaloma, the harms of routinely providing this test to search for occult cancers in patients with unexplained VTE clearly outweigh the benefits.

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This post first appeared on the AFP Community Blog.