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University of Catania, Catania, Italy
Correspondence to: Rossella R. Cacciola, MD, PhD, University of Catania, Via S. Citelli 6, Catania 95124, Italy; e-mail: rcacciol{at}unict.it
To the Editor:
We have read with great interest the recent paper by Rathbun et al (March 2004).1 In their work, they concluded that routine plasma d-dimer measurement has limited benefit as an exclusion test for inpatients with suspected pulmonary embolism (PE).
However, in our opinion, this postulation is seriously flawed by the lack of pretest probability (PTP) assessment with stratification into low-risk, intermediate-risk, and high-risk groups, a critical step in the current diagnostic workup of patients with suspected PE.2 It is well-known that the negative predictive power of the d-dimer test is critically enhanced by the PTP assessment of PE. Both the simplified clinical probability score for PE of Wells et al3 and the Geneva score4 are commonly used to assess PTP in outpatients and inpatients. The combination of clinical probability and d-dimer assay results as the first step in the diagnostic workup for patients with suspected PE has been validated in a number of studies. When a low or intermediate clinical probability was associated with a normal d-dimer level, the negative predictive value for PE was extremely high during long-term follow-up.567
Thus, in the present study by Rathbun et al1 a combination of low or intermediate clinical probability with a normal d-dimer test result could have provided better negative predictive results for PE in their study population. The assessment of PTP by validated clinical scoring systems is accurate and should be the first step in the diagnostic management of patients with suspected PE, as it allows optimization of the further use of resources and the refinement of the probability of PE following noninvasive assays.
References
University of Oklahoma Health Sciences Center, Oklahoma City, OK
Correspondence to: Suman W. Rathbun, MD, MS, University of Oklahoma Health Sciences Center, 920 Stanton L. Young Blvd, WP 3120, Oklahoma City, OK 73104; e-mail: suman-rathbun{at}ouhsc.edu
To the Editor:
We appreciate the comments of Cacciola et al. Our conclusion that d-dimer has a low clinical utility for excluding pulmonary embolism among inpatients with nondiagnostic lung scan findings or negative helical CT scan results is valid because clinical utility does not depend on the pretest probability. We defined clinical utility as the proportion of patients with a negative d-dimer test result. It has been well-documented that a positive d-dimer test result is highly nonspecific and not diagnostically useful. Therefore, our simple point is that most inpatients with nondiagnostic lung scan findings or negative helical CT scan results have positive d-dimer test results. Even if the negative predictive value is 100%, since the d-dimer was rarely negative in inpatients, the clinical utility is low. However, as we stated in our discussion, d-dimer may have greater clinical utility as a first-line screening test, especially in outpatients.
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