BY CHARLES BANKHEAD

A new thrombus-imaging agent may offer help for identifying acute deep vein thrombosis associated with equivocal or negative ultrasound studies in high-risk patients, nuclear medicine specialist Dr. Robert Caretta said during an RSNA scientific session on Monday.

In clinical trials, apcitide demonstrated good sensitivity and specificity for identifying acute DVT. Approved about a year ago by the FDA, the imaging agent binds to platelet glycoprotein IIb/IIIa to mark activated platelets.

"Apcitide images only acute DVT," said Caretta, a radiologist at Roseville Medical Center in Roseville, CA. "It is not a positive test for chronic venous disease. It gives an answer early on, within the first 60 minutes after injection. It can be useful in patients who have negative or equivocal Doppler ultrasound evaluation but who present a high level of clinical suspicion for acute DVT."

Caretta presented data from a study of Tc-99m apcitide scintigraphy evaluations of 243 patients with suspected DVT. The accuracy was in the 75% range overall. When the analysis was restricted to 63 patients who had acute DVT (as confirmed by venography), however, apcitide scintigraphy demonstrated 90.6% sensitivity, 83.9% specificity, 87.3% accuracy, 85.3% positive predictive value, and 89.7% negative predictive value.

Scintigraphic evaluation offers a good adjunct to Doppler ultrasound, which should be considered the standard imaging study for DVT assessment in most clinical settings, Caretta said. The test has good sensitivity in symptomatic patients, is relatively quick, and is inexpensive compared to nuclear studies.

However, ultrasound has low sensitivity in high-risk asymptomatic patients and does not have good sensitivity for thrombi below the knees or for pelvic vein thrombi.

Venography is the most accurate test but is painful, difficult to perform in a swollen leg, and might be technically difficult to interpret in a substantial number of cases.

"I don't think any of us routinely use venography as a screening procedure for acute DVT," Caretta said.

The ability to identify acute DVT quickly and accurately has considerable implications for morbidity and mortality. At least 70% of pulmonary emboli arise from acute DVT in the leg, and pulmonary embolism causes about 100,000 deaths annually, Caretta said. The overall fatality rate for untreated pulmonary emboli is 30%.

Another factor that may help generate interest in the use of Tc-99m apcitide scintigraphy is the fairly recent observation that about 20% of thrombi in the calf propagate above the knee. Almost a quarter of pulmonary emboli might derive from calf DVT, Caretta said.

"When most of us were in medical school or residency, the thinking was that calf DVT didn't have to be treated with anticoagulation but could be treated symptomatically," he said. "The recent clinical literature shows that calf DVT can in fact be a significant clinical problem."