Which initial test is critical for patients presenting with suspected pulmonary embolism?

The D-dimer test is critical for patients presenting with suspected pulmonary embolism because it helps in the initial assessment of the likelihood of a thrombotic event. D-dimer is a fibrin degradation product, and elevated levels can indicate the presence of abnormal clot formation and breakdown in the body. In the context of a suspected pulmonary embolism, a high D-dimer level can suggest that further diagnostic imaging, such as a computed tomography pulmonary angiogram (CTPA), may be warranted to confirm the diagnosis.

While other tests like an electrocardiogram, chest X-ray, and complete blood count can provide valuable information, they are not as critical for the initial workup specifically aimed at confirming or ruling out pulmonary embolism. An electrocardiogram may show signs consistent with a PE but is not diagnostic; a chest X-ray is often normal in cases of PE and will not definitively support the diagnosis; and a complete blood count can indicate anemia or infection but is not specific to clot formation. Thus, the D-dimer test serves as a vital first step in evaluating the likelihood of a pulmonary embolism, guiding further necessary imaging and intervention.