DOES HIGH D-DIMER INCREASE CT USE?

Does an elevated ultrasensitive D-dimer level in a patient whose pre-test probability puts him at low risk for pulmonary embolus (PE) indicate an increased risk for PE or deep venous thrombosis (DVT)? Does the elevated D-dimer require chest CT and/or Doppler studies? If chest CT is warranted in this situation, doesn’t the ultrasensitive D-dimer increase rather than decrease the use of CT in the low-risk pre-test probability patient?
—Matthew Datzman, MD, Eldorado, Ill.

During the past decade, multiple relatively large-scale studies have examined diagnostic algorithms in the context of clinical suspicion of PE. Several of the more recent trials have demonstrated the utility of D-dimer assays when used in conjunction with other noninvasive strategies (Lancet. 1999;353:190-195). The limitation of D-dimer is directly related to its lack of specificity, given that levels are elevated in conditions other than PE (malignancy, status post surgery, and even with age). However, D-dimer retains a high degree of negative predictive value. Thus, having a negative or normal D-dimer level in a setting of low clinical suspicion is quite helpful. The situation described is perhaps the most challenging: an elevated D-dimer with a low clinical suspicion. In this case, one would likely be forced to consider further noninvasive diagnostic approaches. The Christopher Study Investigators recently published a prospective cohort examination of >3,000 patients with suspected PE. The investigators used a combination of a dichotomized version of the Wells clinical decision rule (PE “likely” vs. “unlikely”) along with D-dimer testing and CT scanning. In the context of a clinical judgment of “unlikely” PE and an elevated D-dimer, patients were referred for CT scan. Thus, the performance of CT scans was in fact increased by the presence of an elevated D-dimer. In the final analysis, however, the strategy was highly effective in diagnosing PE without the use of invasive testing (JAMA. 2006;295:213-215).
—Christopher Ruser, MD (116-11)

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