University of Missouri-Columbia Columbia, MO
Correspondence to: Ousama Dabbagh, MD, Chief Fellow, Division of Pulmonary, Critical Care Medicine, University of Missouri-Columbia, One Hospital Dr, MA417, Columbia, MO 65212; e-mail: DabbaghO@health.missouri.edu
We enjoyed reading the article by Paterson and Schwartzman in CHEST (June 2001),1 concluding that “spiral CT can replace pulmonary angiography in patients with nondiagnostic V̇/Q̇ [ventilation/perfusion] scans.” We wish to raise several issues regarding these recommendations.
This conclusion is based solely on a hypothetical model that does not represent actual clinical practice and decision making. We think that adopting their diagnostic approach may not be sufficient to exclude clinically significant pulmonary embolism. Furthermore, this could potentially lead to unnecessary treatment or lack of appropriate anticoagulation.
First, there are known issues surrounding subsegmental pulmonary emboli. It is known that the sensitivity of spiral CT in this area is not high. Relying on spiral CT in these situations may result in missing small peripheral clots and their potential impact on patients with limited cardiopulmonary reserve.
Second, the differences among radiologists in interpreting helical CT, especially in centers with less experience, are considerable. This fact was not discussed in this article or taken into account in their model.
Several investigators have studied the role of the d-dimer test in the workup of pulmonary embolism. We are glad that the authors referred to d-dimer in their discussion. Dabbagh et al2 studied the correlation between spiral CT of the chest and d-dimer latex agglutination test (Accuclot; Sigma Diagnostics; St. Louis, MO) among 79 patients (77% women). They found that a negative d-dimer result (< 0.25 μg/mL) highly predicted a negative spiral CT of the chest result (negative predictive value, 100%). We believe that spiral CT scan of the chest might not be necessary in the presence of a negative d-dimer test result by latex agglutination.
Although we believe that spiral CT of the chest can be very helpful in the evaluation of pulmonary embolism, we do not think it is the complete and final answer.
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