D-Dimer Test May Replace 60% of CT Lung Angiograms

The use of a D-dimer test as the first step in the diagnosis of blood clots in the lungs could eliminate the need for up to 60% of all computed tomography (CT) angiograms of the lungs, according to a new study by researchers at the Kaiser Foundation Hospital in Honolulu (HI, USA).

D-dimer tests measure the amount of D-dimer in a patient's blood. D-dimer is a breakdown product of the protein fibrin, which is found in blood clots. People with an unusual amount of D-dimer in their blood presumably have blood clots somewhere in their body.

The study looked at 426 patients who underwent both CT angiography of the lungs and D-dimer level evaluation. A total of 84 of those patients had negative findings on D-dimer, 82 of whom also had negative findings on CT angiography. The remaining two had indeterminate findings on CT. Among patients with positive D-dimer tests, no one with a level between 0.4 and 1.0 µg/ml had positive findings for blood clots on CT angiography.

"In our retrospective analysis, we found that people who did not have an elevated amount of D-dimer in their body did not have blood clots in their lungs detected by CT, remarked Hyo-Chun Yoon, M.D., an author of the study. "In addition, we found that even people with an elevated D-dimer did not have blood clots in their lungs detected by CT if their level was abnormal but not very high, in our case 1.0 µg/ml. If we had used a cutoff value of 1.0 µg/ml, we may not have needed to do up to 60% of those CT angiograms. However, some of these patients may still have benefitted from a chest CT based on their presenting clinical situation.”

According to Dr. Yoon, the outcome of this study could have significant benefit to patients. "Although CT studies are helpful in the appropriate situation, they do expose patients to significant radiation, require the use of a contrast agent that can be toxic to the kidneys, and are quite expensive. We would like to see a prospective study done which confirms our findings before we firmly advocate anything, but I think the D-dimer will
significantly reduce the number of CT studies that are performed for blood clots in the lungs.”

This study appears in the June 2004 issue of the American Journal of Roentgenology.