What is the next step in evaluating a patient with colon cancer, presenting with sharp chest pain, shortness of breath, tachycardia, and right leg swelling, for potential pulmonary embolism (PE)?

Next Step in Evaluating This Patient for Pulmonary Embolism

This patient with colon cancer presenting with tachycardia, chest pain, dyspnea, and unilateral leg swelling has a high pretest probability for PE and should proceed directly to CT angiogram of the chest (Answer A) without D-dimer testing. 1

Risk Stratification Determines the Diagnostic Pathway

This patient has multiple high-risk features that place them in the high pretest probability category (>40%):

• Active malignancy (colon cancer) - a major risk factor present in 80-90% of PE patients 1
• Tachycardia (pulse 110) suggesting physiologic stress 2
• Unilateral leg swelling indicating likely deep venous thrombosis 2
• Classic cardiopulmonary symptoms (sharp chest pain and dyspnea) 1

The American College of Physicians explicitly states that clinicians should obtain imaging with CT pulmonary angiography in patients with high pretest probability of PE and should NOT obtain a D-dimer measurement in this population. 1

Why Not D-Dimer? (Answer B is Wrong)

D-dimer testing is contraindicated in high-risk patients for several critical reasons:

• D-dimer is only useful for ruling out PE in low or intermediate pretest probability patients 1
• In high-risk patients, a negative D-dimer does not change management - imaging is still required 2
• D-dimer has limited value in cancer patients because malignancy itself elevates D-dimer levels regardless of thrombosis 1
• Ordering D-dimer in this scenario wastes time and delays definitive diagnosis 2

Why Not Echocardiogram First? (Answer C is Wrong)

Echocardiography is reserved for hemodynamically unstable patients (systolic BP <90 mmHg) to assess for right ventricular dysfunction and guide thrombolytic therapy decisions. 2, 3

This patient has a blood pressure of 130/76, making them hemodynamically stable. The American College of Radiology guidelines specify that CT pulmonary angiography is the primary imaging modality for stable patients with suspected PE. 1

Why Not Leg Ultrasound First? (Answer D is Wrong)

While lower extremity ultrasound can be useful as an adjunctive test when CT is contraindicated (renal failure, contrast allergy, pregnancy), it should not replace CT angiography as the initial diagnostic test in this stable patient. 2

The British Thoracic Society does recommend leg vein imaging as a first-line investigation in specific circumstances: patients with previous PE, clinical DVT, or chronic cardiorespiratory disease. 1 However, even with unilateral leg swelling present, the American College of Physicians' more recent (2015) guidelines prioritize direct CT angiography in high-risk patients to definitively diagnose or exclude PE. 1

Finding DVT on ultrasound would confirm the need for anticoagulation but would not rule out concurrent PE, which requires different management considerations regarding hemodynamic stability and potential thrombolysis. 2

CT Angiography as the Gold Standard

Multidetector CT pulmonary angiography has become the primary imaging modality for evaluating suspected acute PE, with sensitivity of 95% or higher for segmental or larger emboli. 1

The ACR Appropriateness Criteria designate CTPA as the definitive test for patients with high clinical probability, reserving ventilation-perfusion scans only for patients with contraindications to CT or when CT is unavailable. 1

Critical Pitfall to Avoid

Skipping pretest probability assessment leads to overdiagnosis of clinically insignificant subsegmental PEs and exposes patients to unnecessary anticoagulation risks. 2 However, in this case, the clinical presentation is unambiguous - this patient clearly falls into the high-risk category requiring immediate definitive imaging.