We must express serious concerns about the internal validity and conclusions of the recent paper by Egermayer et al¹ in which the authors suggest that normal results of D-dimer, arterial blood gas tensions, and respiratory rate measurements can be used to rule out pulmonary embolism. With respect to blood gases, two earlier well designed studies reported that the PaO₂ and PaCO₂, alone or in combination, did not exclude pulmonary embolism.^2 3 If a low PaCO₂ is taken as a reasonable surrogate for tachypnoea, these studies directly contradict Egermayer's findings. We attribute this discrepancy to a serious flaw in study design.

In any valid evaluation of the accuracy of a diagnostic test, comparison must be made with an appropriate reference standard.⁴ Being able to conclude that any test can exclude pulmonary embolism, as the authors have done, mandates that the selected reference standard accurately and objectively rules . . . [Full text of this article]